CRINOIDEA AND ECHINOIDEA 



31 



seen. It is about 7 mm. in diameter and 4 mm. high and is de- 

 nuded of all its spines. The peristome is relatively very large 

 as it is about 3.75 mm. across; except for the primordial 

 ambulacrals it is almost completely free from plates. The 

 abactinal system is less than 3 mm. across but ocular I is 

 broadly insert. The ambulacra are very simple and quite 

 echinoid with the pores in regular arcs of 3; the only peculiar- 

 ity is that, above the ambitus, every other primary ambulacral 

 tubercle on each side is distinctly smaller or may even be sup- 

 pressed. 



In the Narrative this species is referred to as occurring 

 at the Tortugas (p. 133) where it is said to be ''much larger" 

 than in the Bahamas. In the latter region, it is referred to 

 as occurring at a flat bar near the mainland of Eleuthera 

 (p. 202) and at Spanish Wells (p. 213). On pp. 213 and 214, 

 Professor Nutting records some very interesting and important 

 observations which go to show that this sea-urchin exercises 

 ' ' choice ' ' and has at least a rudimentary ' ' memory. ' ' 



Bahamas: Eleuthera Island, Spanish Wells. 4 adult speci- 

 mens. 



Bahamas: Eleuthera Island, Harbor Island. 2 adult speci- 

 mens 



Locality unknown. 1 very small specimen. 



Trigonocidaris albida 



A. Agassiz, 1869. Bull. M. C. Z., /, p. 263. 1872, Eev. Ech., pi. IV, figs. 

 1-7. 



In the "Narrative" (p. 174) Professor Nutting speaks of 

 this pretty little sea-urchin being abundant on the Pourtales 

 Plateau. There are nearly a hundred specimens in the collec- 

 tion but the great majority lack a locality label. There is no 

 doubt however that they are from the Pourtales Plateau. They 

 range in diameter from 6 to 13 mm., the latter being about the 

 maximum size for the species. The growth changes after the 

 diameter is 6 mm. seem to be very slight. Even the peristome 

 shows only a small relative decrease; it is 3 mm. across (50%) 

 in the smallest specimen and 5.5 mm. (42%) in the largest. 

 The amount of sculpturing on the test does not seem to vary 



