1890.] NATURAL SCIKNCES OF l'HILADKI>l'ir[A. o29 



but a local variety. The typical form is seen in the figure sjiven 

 by Professor Alexander Agassiz in his Revision of the Echini. 



This species is found in the West Indies, extending northward as 

 far as Cape Hatteras, and southward to Itabapuana, (100 m. N. E. 

 Rio Janeiro) Brazil. 



Professor Verrill in his Report u])on the Invertebrata of Vineyard 

 Sound says that the specimens found north of Cape Hatteras are 

 rare and dead. 



Thyraster serpentarius, Mullor unJ Troschel. 



Kchinaster serpeiitarius (Val.) Muller and Troschel, .System iler Asteriilen, |i. 24. 

 Perrier, Arch. Zool. Exper., t. iv, p. 370. 



A single specimen of this interesting form was collected at Vera 

 Cruz. It corresponds well with Miiller and Troschel's description. 

 'They described their species from specimens in the Paris Museum, 

 also obtained from Vera Cruz. The specimen collected by the ex- 

 pedition is superficially characterized by the numerous very small, 

 short, blunt spines forming irregular longitudinal and transverse 

 rows upon its dorsal surface, and by the peculiar arrangement of the 

 arabulacral spines. There are four of these spines arranged in a 

 row upon the aboral edge of each adambulacral plate. The inner- 

 most spine is the smallest and bears at its base a rudimentary spine- 

 let. Each })late of the .series of ventral plates adjoining the adam- 

 bulacral plates has three or four spines upon its aboral edge. Each 

 of the lateral plates also has a row of three spines upon its aboral 

 edge. The ambulacral, ventral and lateral spines of the arms are 

 verj' small, but not so small as tho.se of the dorsal surface. The 

 distal portions of all the spines have a rough appearance when 

 viewed with the naked eye. and when examined with the microscope 

 are seen to be thorny. The reticulated, skeleton is made up of a 

 number of qudrilateral plates, connected at their angles and arranged 

 in longitudinal rows. The abactinal spines are borne upon the edges 

 of these plates. 



The ventral and lateral plates are connected by an intermediate 

 ossicle. Intermediate ossicles occasionally occur between the other 

 plates of the skeleton. The central portion of the surface of these 

 j)lates is covered with minute tubercles which give them a gran- 

 ulated appearance. Figs. 19, 20 and 21, PI. VIII, represent dorsal, 

 ventral and lateral views of a portion of the skeleton of an arm, en- 

 larged about four diameters. 



