114 S. I. Smith on American Crustacea. 



lateral angle being more developed on the side of the larger cheliped. 

 The ocular peduncle also is usually longer on this side, and in some 

 species is terminated by a slender stylet. This ocular stylet is quite 

 remarkable, and appears to be a constant and important character of 

 several species. Desmarest mentions it in a species which he de- 

 scribes under the much misapplied name of vocans, but his descrip- 

 tion would imply that it was found ui)on both sides. Edwards, in his 

 description of G. styliferus, mentions it, and it is represented in his 

 figures, but his words also imply that it was not confined to one side. 

 In Edwards' Ilistoire naturelle des Crustaces, tome ii, p. 50, however, 

 there is the following foot note : — " Au moment de mettre cette feuille 

 sous presse ; je re9ois de M. T. Bell la communicatioi\ d'un fait que je 

 ne puis passer sous silence. Quelques Gelasimes presentent, a un cer- 

 tain age, sinon toujours, un stylet a I'extremite du pedoncule oculaire 

 du cote de la grosse pince, tandis que I'oeil du cote oppose conserve 

 toujours la forme ordinaire." This observation of Bell agrees with 

 my own on quite a number of specimens of two species described be- 

 yond, and it is quite probable that this is always the case. 



The described species of Gelasiimis, as limited by Edwards and 

 other authors, form two very natural and distinct groups, which 

 should perhaps be recognized as genera, but upon which, for the pur- 

 poses of the present paper, it is not necessary to impose new names. 



In the first group the front is contracted between the ocular pedun- 

 cles so that their bases approach very closely, and the peduncles them- 

 selves are very long and slender. This includes Edwards' section A, 

 in which the front is spatulate, and probably also, all of his section B, 

 in which the front is very narrow between the eyes but not spatulate. 

 In some of the species the meral segments of the ambulatory legs are 

 armed with sharp sj)ines, and with these species I have united the ge- 

 nus Acanthojylax. 



In the second group, which corresponds with the section C of Ed- 

 wards, the front is broad and evenly arcuate, and the bases of the 

 ocular peduncles are thus sejiarated by quite a broad space. The 

 peduncles themselves are much shorter than in the species of the other 

 section. The species are mostly small and exhibit a remarkable uni- 

 formity in general appearance, so that it is difficult to distinguish 

 them without careful study. 



A single species, described beyond, differs from both these groups, 

 in having the male abdomen only five-jointed and not narrowed at 

 the second segment. The carapax is transverse and very little con- 

 tracted behind. This species is evidently the type of a third very 

 distinct group. 



