RHYNCHOPYGUS CARIBAEARUM. 343 



Rhynchopygus caribaearum 



! Cassidulus caribaearum Lamk 1801. An. s. Vert. 

 ! Rhynchopygus caribaearum LuTK. 1864. Bid. til Kmxls. 



PL XV /. 1-4. 



Mr. Pourtales brought home fragments of this species showing that it must 

 equal in size its Pacific representative. As it has been figured frequently, and 

 described so well by Liitken, I will only call attention to a few points of dif- 

 ference between the East and West Coast species. The bare actinal band of 

 the West India species is deeply pitted with longitudinal, round and elliptical 

 pits and furrows (PL XV f. 3), the edges surmounted by minute tubercles, 

 carrying extremely delicate spines, resembling in every respect the structure 

 of the microscopic spines of the fascioles of the true Spatangoids. This band 

 is broad and elliptical, in the West India species, in the posterior actinal part 

 of the test, while in the Pacific species it is narrow even near the actinostome, 

 tapering very rapidly to a point near the anal extremity. The plates of the 

 anal system, arranged in three rows, are broader and longer than in the 

 Pacific species, where they are arranged in two rows only, the outer row 

 being the largest. In the Pacific species the pits of the smooth band are 

 reduced to a few indistinct impressions, the whole band being thickly covered 

 by minute silk-like spines. The floscelle is most distinct also, while, owing 

 to the sculpture of the bare band round the mouth in the West India species, 

 its outline cannot always be distinctly traced. 



There are unfortunately no specimens of these two species of the same size 

 in any of the collections I have examined, making a more accurate com- 

 parison impossible ; the Pacific species, being evidently full grown, will be 

 described at greater length. Tbe difference in the length of tbe poriferous 

 zones both of the anterior and the posterior lateral ambulacra, so marked in 

 the Pacific species, exist already in the smallest specimen, about three quar- 

 ters of an inch in length, which I have examined. No pedicellarise have 

 been detected in this species. 



Fragments in 106 fathoms. 



