MUSEUM OF COMPARATIVE ZOOLOGY. 149 



The abdomen of the male is naked, smooth, and polished, and the ster- 

 num is granulated. 



Dimensions of an adult male: Length of earapax, 0.37; breadth, in- 

 cluding spines, 0.84 : excluding spines, 0.50 inch: proportion of length to 

 latter breadth, l : 1.35. In a young male the length of the earapax is 

 0.25; breadth, including spines, 0.55; excluding spines, 0.34 inch. 



This species is easily recognized among mosl of its congeners by its 

 lime; carpal spines. From .!. Ordwayi and A. tumidtdus it is distin- 

 guished by the great length of the lateral spines. 



Oil' the Tortugas, January 4, 1868. Cast No. I. 13 fathoms 



Off Carysfort Reef, March "21, 1869. Cast No. 7. 40 



Off Conch Reef, May 11, 1SG9. Cast No. 3. 4'.i 



Off Alligator Reef, May 8, 1869. Cast No. 3. 53 



Off Pacific Reef, May 13, 18G9. Cast No. 3. 60 



Lat 31° 31', Long. 79° 41', May 25, 1868. Cast No. l. 74 



Off American Shoal, May s, IS68. Cast No. 3. 150 



Achelous tumidulus nov. sp. 



Carapax rather narrow, only one fourth broader than long, rather more 

 convex than is usual in the genus, and somewhat protuberant about the 

 middle and posteriorly. Posterior tooth of the antero-lateral margin 

 (lateral spine) of moderate length, about as long as the space occupied by 

 the three teeth next in trout of it. Front prominent, projectile: much 

 beyond the level of the outer angles of the orbits, convex ; teeth rounded, 

 the two middle ones being smaller and most prominent, and separated 

 from the lateral ones by a rather broad, shallow sinus. Xo notch on the 

 orbital margin above the insertion of the external antenna'. Meros-joint 

 of the outer maxillipeds longer than broad. Chelipeds rather short; 

 meros armed with three large and one small spine on the front edge; 

 spine of the outer extremity of the posterior edge of the meros almosl 

 obsolete. Inner spine of the carpus long, reaching to the middle of the 

 palm of the hand. There is only one spine on the superior margin of the 

 hand. On the meros-joint of the posterior p-ur of ambulatory feet there 

 is a denticulated extero-inferior margin, but no spine. The abdomen of 

 the maie is smooth and polished. 



Dimensions of a, male: Length of earapax, 0.20: breadth, including the 

 lateral -pine-. 0.31 ; excluding the spines, 0.25 inch; proportion of length 

 to latter breadth. I : 1.25. 



This differs from most other American species heretofore described in 

 the narrowness of the carapax and the prominence of the front. From .I. 

 Ordicayi it differs in the frontal teeth, which are not deeply cut. 



West of Tortupas, January 16, 1869. Cast No. 8. 37 fathoms. 

 Off Conch Reef, March 21, 1869 Cast No. 1 10 



