Dytiscidae

Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), Zootaxa 3666 (2), pp. 137-159 : 153-154

Key to the genera of Mesozoic Dytiscidae (adults)

1. Metaventrite with straight posterior margins of lateral lobes, converging posteriad at obtuse angle ( Fig. 23 ); elytra with dark stripes (subfamily incertae sedis).................................................................. Sinoporus.

- Metaventrite with concave posterior margins of lateral lobes (e.g., as in Fig. 20 ); elytra without dark stripes............. 2.

2. LC/LV (ratio of maximum length of metacoxal plate and lateral lobe of metaventrite, both measured longitudinally, as in Fig. 22 ) around 1–1.7 (Liadytiscinae).......................................................................... 5

- LC/LV around 2 or greater (subfamily incertae sedis).......................................................... 3

3. Posterior and anterior margins of lateral lobe of metaventrite strongly converging, then slightly diverging again, then converging again near epipleuron; LC/LV around 3............................................. " Palaeodytes " incompletus .

- Posterior and anterior margins of lateral lobe of metaventrite more or less evenly converging towards epipleuron......... 4.

4. LC/LV around 3 (as in Figs 19, 20 )................................................................ Cretodytes .

- LC/LV around 2.............................................................................. Palaeodytes .

5. Metacoxal lines weakly diverging anteriad; metacoxal processes with incision between them, conjointly truncate or rounded posteriorly, not narrowed anteriad (as in Figs 6, 7 ); LC/LV around 1; metatibia narrow and long, longer than metafemur (Liadytiscini)........................................................................................ 6.

- Metacoxal lines strongly diverging anteriad; metacoxal processes slightly narrowed anteriad, with posterior margins rounded (as in Figs 8–11 , 12, 14 ); LC/LV around 1.2–1.7; metatibia subequal in length to or shorter than metafemur (Mesoderini trib. n.)................................................................................................. 8.

6. Metacoxal processes conjointly truncate posteriorly, with incision between them; metaventrite with laterally limited elevated median area triangular......................................................................... Liadytiscus.

- Metacoxal processes conjointly truncate apically, with incision between them, or rounded with incision; metaventrite with elevated median area rounded or without such elevated area..................................................... 7.

7. Metacoxal processes more or less conjointly truncate posteriorly, with posterior margins appearing somewhat sinuate, with incision between them (as in Figs 6, 7 )...................................................... Liadyxianus gen. n.

- Metacoxal processes rounded.................................................................. Liadroporus.

8. Metaventrite with rounded laterally limited elevated median area ( Figs 8–11 )............................... Mesoderus.

- Metaventrite without laterally limited elevated median area ( Figs 12, 14 )............................. Mesodytes gen. n.

Figures

FIGURES 22 – 24. (22) Ilybius adygheanus Petrov, Shapovalov & Fery, 2010: metaventrite and metacoxa, with measurements WC, WS, LC and LV shown; modified from Petrov et al. (2010); (23) Sinoporus lineatus Prokin & Ren, 2010: holotype in ventral view, redrawn and modified from original description with LC and LV shown (in this case the longest point of the lateral lobe of the metaventrite is at the very base of the lobe; it has been measured immediately lateral of the posterior margins of the mesocoxa, i. e., at the very base of the lobe, if we define the lobe as the part of the metaventrite lateral of the mesocoxa); (24) Lancetes lanceolatus (Clark, 1863): metaventrite of recent specimen from Lake Cronin (Western Australia); arrow indicates impression at lateral margin of median elevated area of metaventrite.

FIGURES 19 – 21. Cretodytes incertus sp. n.: (19) photo of holotype, (20) line drawing of holotype; (21) Angaragabus jurassicus Ponomarenko, 1963: photo of holotype, PIN 1670 / 390.

FIGURES 5 – 7. (5) Liadytes aspidytoides sp. n., photo of specimen PIN 2470 / 945; Liadyxianus kirejtshuki sp. n.: (6) photo of holotype, (7) line drawing of holotype.

FIGURES 8 – 11. Mesoderus punctatus sp. n.: (8) photo of holotype, (9) line drawing of holotype; arrow indicates penis; Mesoderus ovatus sp. n.: (10) photo of holotype, (11) line drawing of holotype.

FIGURES 12 – 15. Mesodytes rhantoides sp. n.: (12) photo of holotype, (13) line drawing of holotype in dorsal view, (14) line drawing of holotype in ventral view, (15) photo of holotype (fragment, 3 × enlarged): male genitalia; arrows indicate base, dorsal margin and apex of penis.