Herbert L. HawJdns — Studies on the Echinoidea. 491 



deep-sea exploration that has been achieved since 1888. Further 

 discussion of its characters and affinities must needs be based on new 

 knowledge of its alleged relatives. 



The following is an abridged account of its salient features taken 

 from Loven's description : — 



Length ..... 3-5 mm. 



Breadth ..... 3 -41 mm. 



Height 2 -16 mm. (0-62 of length). 



Peristome diameter . . . [1-015 mm.] (0-29 of length). 



Corotia. — Obscurely subpentagonal ; tumid. 



Apical system. — Wanting, apparently central in position. 



Peristome. — Central, very slightly invaginated. Outline irregularly 

 circular. The epistroma not extending quite to the margin, leaving 

 a delicate inner rim in which occur narrow branchial (?) incisions. 

 Interradial margins built of large, single primordial interambulacrals. 

 Ambulacral margins built of high, narrow primordial ambulacrals. 

 Externally each ambulacral bearing a large " epistromal prominence " 

 with a glossy and minutely punctate surface, the pairs of these 

 meeting adorally to a large, single, perradially situate sphseridial pit. 



Perignathic girdle. — Paired ambulacral processes of slightly 

 •cuneiform shape, expanding distally, meeting the floor of the test at 

 a very acute angle. The processes are apparently placed over the 

 adradial sutures. The figure (Loven, pi. i, fig. 5 ; here PI. XVII, 

 Fig. 2) is hard to understand. It gives the appearance of a specially 

 intercalated plate as the foundation of each process, a most anomalous 

 condition. Possibly the apparent sutures represent the raised edges 

 of the articulation between the processes and the corona. There 

 seem to be no interradial perignathic elements. 



Periproot. — Mostly broken away, but apparently projecting into 

 interambulacrum 5 almost to the ambitus. Posterior margin broad 

 and symmetrical. 



Ambulacra. — Composed of simple, rectilineal plates throughout. 

 No biporous plates. (In Loven, pi. i, fig. 5, the proximal ambulacral 

 in column IIIJ seems to show two pores; but this is in contradiction 

 to the statements in the text, and is probably due to an error in 

 drawing or printing.) Pore-pairs confluent, dissimilar ; external pore 

 round, internal pore slit-like ; placed near the adapical transverse 

 margins of the plates. Peripodia sunken. 



Interanihdacra. — Built of normal, mostly unituberculate plates. 

 Proximal unpaired plate very large, variable in size and shape in the 

 several areas. In Loven's figure (here PI. XVII, Fig. 2) plate \a. 2, 

 is shown to be low and cuneiform, tapering towards the interradial 

 suture. Similarly placed plates in other areas tend towards this 

 character. 



Ornament. — Primary tubercles large, scrobiculate, crenulate, and 

 with perforate maraelons. Appi'oximately similar in size on inter- 

 ambulacra and ambulacra, and in both arranged in regular series. 

 Surface of both areas thickly studded with glossy, ovoid pi'otuberances, 

 often grouped into scrobicular circles around the main tubercles. 



Hahiiat. — Near Virgin Islands, between 200 and 300 fathoms. 



