Symethoides monmouthorum, Van Bakel & Guinot & Artal & Fraaije & Jagt, 2012

Van Bakel, Barry W. M., Guinot, Danièle, Artal, Pedro, Fraaije, René H. B. & Jagt, John W. M., 2012, A revision of the Palaeocorystoidea and the phylogeny of raninoidian crabs (Crustacea, Decapoda, Brachyura, Podotremata) 3215, Zootaxa 3215 (1), pp. 1-216 : 106-107

Symethoides monmouthorum n. sp.

Notopocorystes cf. N. tridens — Landman et al. 2007, p. 29, fig. 15N, O.

( Fig. 33A–D )

Diagnosis. As for genus.

Derivation of name. In honour of the Monmouth Amateur Paleontologist's Society (New Jersey, U.S.A.), of which Ralph Johnson is a member, for bringing this specimen to our attention.

Material examined. One partly decorticated carapace from the top of the lower Danian Tinton Formation , Manasquan River Basin , Monmouth County, New Jersey, U.S.A. ( AMNH 50421 ) .

Description. Carapace small, fusiform, about twice as long as broad, widest at mid-length, strongly convex in transverse cross section, slightly convex in longitudinal cross section, uniformly covered with granules, coarsest towards orbitofrontal, anterolateral regions. Orbitofrontal margin narrow. Broad base of rostrum with prominent ridge extending posteriorly about one-third of total carapace length, bounded by 2 deep grooves effacing posteriorly. Convex anterolateral margin with diminutive, anteriorly directed spine at approximately one-fifth of total carapace length from front. Subhepatic region with blunt crest.

Posterior margin slightly wider than orbitofrontal margin. Branchiocardiac grooves curved, situated slightly posterior of mid-length. Pterygostome elongated, convex, covered by evenly spaced, fine granules; buccal margins concave, with smooth rim; posterior corner of pterygostome recessed for mxp3 coxa. Branchiostegite low posteriorly, with pronounced border.

Remarks. Despite the superficial resemblance to Lyreidinae , Symethoides n. gen. differs markedly from Lyreidus , Lysirude and Macroacaena in having an anterior axial ridge bounded by two grooves and a completely granular carapace, and in lacking long anterolateral spines (few exceptions in Lyreidus ). It differs also from Macroacaena in lacking a posterior ridge and a narrower orbitofrontal region. The latest Cretaceous Lyreidina Fraaye & Van Bakel, 1998 , shows an anterior axial ridge, but differs by its pyriform shape, carapace areolation and ornament. From all currently known raninids, the new genus is distinguished by a unique combination of carapace outline, frontal region and ornamentation. The fusiform carapace, small, forwardly directed anterolateral spine and narrow orbitofrontal region support assignment to the subfamily Symethinae .

Figures

FIGURE 33. A–D. Symethoides monmouthorum n. gen., n. sp. (Raninidae, Symethinae), lower Paleocene (Danian), Monmouth County, New Jersey (U.S.A), AMNH 50421 (holotype); dorsal view of carapace, left lateral view, frontal view, and ventral view showing pterygostomes. Scale bar: 5mm.