588 Tlie Fossil Crab of Gay Head. 



lateral carapax, this character is not in them accompanied 

 by the form of orbit alluded to, which indicates consider- 

 able length in the ocular peduncles. In the outer maxilli- 

 peds, and in the shape and anterior breadth of the ster- 

 num, we have an unmistakable resemblance to the Portu- 

 nidae ; but in the seven-jointed male abdomen we find a 

 return to the Ocypodoid character, for that part of the 

 body in all male Portunids is five-jointed. 



With regard to the more intimate relations of Archaeo- 

 plax, it may be remarked that while the shape of the cara- 

 pax and its postero-lateral depressions or channels are the 

 same as in the Carcinoplacidae, the orbits and antero-lateral 

 margins more closely resemble those of Prionojjlax, a genus 

 of Gonoplacidae. But our genus is removed from the latter 

 family by the form of the posterior segment of the sternum, 

 which is not " debordant " or exposed on either side beyond 

 the abdomen, this being, in Gonoplacidae, narrow at the 

 base. From the genera of Carcinoplacidae already known, 

 the new fossil genus differs as follows : — From Eucrate* 

 which it exactly resembles in the shape of the front, it dif- 

 fers in its elongated orbits, and broader male abdomen. 

 From Pseudorhombila, — to which I have already alluded 

 as having similar dhelipcds, — in the form of the orbits and 

 antero-lateral margin. From Carcinoplax and Pilumno- 

 plax, it also differs in the character of the orbits. Finally, 



* Professor Dana has misapprehended the genus Eucrate of De Haan, in placing 

 it in the Gonoplacidae, having been very naturally misled by that author's neglect 

 to give the position of the genital appendages of the male, a point of the highest 

 importance. The resemblance to the Gonoplacidae in De Haan's genus, is indeed 

 gi'eat; but I have recently had occasion to examine, in the ^luseum of Compar- 

 ative Zoology, wet specimens of Eucrate ci-enatus, the typical, and indeed the only 

 species yet known, in wliich I find that the male organs arise from the coxas of 

 the posterior feet, and are not " e sterno ortaj abdominisque tccta;," as given in 

 Dana's diagnosis of the genus (Crustacea of the U. S. Kxploring Expedition, I. p. 

 310). The crab, therefore, will falKinto the Carcinoplacidae. The Eucrate crassi- 

 manus of Dana, having sternal verges, is, therefore, not a true Eucrate, but will be 

 the type of a new geims, upon wliich I will not here impose a name, but merely 

 point it out for the bcuelit of whomsoever may hcicaftcr monograph the group. 



