Bournelyreidus eysunesensis ( Collins & Wienberg Rasmussen, 1992 ) 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 : 79

Bournelyreidus eysunesensis ( Collins & Wienberg Rasmussen, 1992) n. comb.

Hemioon eysunesensis Collins & Wienberg Rasmussen, 1992: 19 .

Remarks. Hemioon eysunesensis (see Collins & Wienberg Rasmussen 1992: 19, fig. 10a–c), based on 82 specimens from the upper Campanian of Nûgssuaq (West Greenland) and originally referred to Raninidae , should be reassigned to Lyreididae and a new genus, Bournelyreidus n. gen., for which it becomes the type species.

The anterolateral margin bears two spiniform teeth and the rostrum is excavated and bifid. The pterygostome is strongly tumid, with ‘a ridge running parallel to the pleural suture’ ( Collins & Wienberg Rasmussen 1992: 21). The anterior sternites, at least sternite 3, forms a distinct crown. The anterior part of sternite 4 is expanded laterally, where it incises the rather large mxp3 coxa; the posterior corner of the pterygostome is recessed for the rounded distal margin of the mxp3 coxa ( Collins & Wienberg Rasmussen 1992: 20, fig. 10c). Sternite 5 is laterally extended to join the exposed pleurites. The fourth abdominal somite bears a prominent tubercle, and the sixth abdominal somite is long ( Collins & Wienberg Rasmussen 1992: 21), both characters typical of Lyreididae . Projections arising from sternite 5 have not been illustrated nor noted in the original description.

The P5 are ‘more dorsally placed, smaller, less flattened and have only a small paddle-like dactylus’ ( Collins & Wienberg Rasmussen 1992: 22). Such fragile details are rarely seen in the fossil record, and because the type series is exceptionally well-preserved and there are many specimens ‘…preserving details of the ventral surface and limbs’ ( Collins & Wienberg Rasmussen 1992: 21), the type series of B. eysunesensis should be re-examined in order to document as many data as possible.

Remarks. Palaeocorystes laevis (see Schlüter in von der Marck & Schlüter 1868: 298, pl. 44, fig. 2), from the upper Turonian to upper Santonian of northern Germany, was referred to Hemioon by Collins (1997: table 1). An additional specimen, recently recognised in the RME collections, allows this poorly illustrated species to be reassessed. It shows the following characters which are typical of Bournelyreidus n. gen.: posterolateral margin with divergent and vertical portion; rostrum excavated and bifid; outer orbital tooth developed; orbital margin horizontal; cuticle with scattered pits, small granules (upright nodes) near the lateral margin. The posterior lateral spine is rather well developed for the genus and the branchiocardiac grooves are obsolete. Bournelyreidus laevis closely resembles B. eysunesensis .