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 carapax, 0.37; breadth, in- 

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

 latter breadth, 1 : 1.35. In a young male the length of the carapax is 

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



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

 long carpal spines. From A. Ordwayi and A. tumidulus it is distin- 

 guished by the great length of the lateral spines. 



Off the Tortugas, 



January 4, 1868. 



Cast No. 



1. 



13 fathoms. 



Off Carysfort Reef, 



March 21, 1869. 



Cast No. 



7. 



40 



M 



Off Conch Reef, 



May 11, 1869. 



Cast No. 



3. 



49 



« 



Off Alligator Reef, 



May 8, 1869. 



Cast No. 



3. 



53 



u 



Off Pacific Reef, 



May 13, 1869. 



Cast No. 



3. 



60 



" 



Lat 31° 31', Long. 79° 41' 



, May 25, 1868. 



Cast No. 



1. 



74 



« 



Off American Shoal, 



May 8, 1868. 



Cast No. 



3. 



150 



ct 



Acheloiis 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 front of it. Front prominent, projecting 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. No notch on the 

 orbital margin above the insertion of the external antennae. 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 almost 

 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 pah- of ambulatory feet there 

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

 the male is smooth and polished. 



Dimensions of a male : Length of carapax, 0.20 ; breadth, including the 

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

 to latter breadth, 1 : 1.25. 



This differs from most other American species heretofore described in 

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

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



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

 Off Conch Reef, March 21, 1869. Cast No. 1. 40 " 



