106 VERRILL 



lower marginal plates are similar and equal in number, but more 

 regular. Each bears a single spine much like the dorsals in size and 

 form. Below this row there is a wide naked channel with large 

 papular areas, like those above it. Between this row and the adambu- 

 lacral plates there is only one row of plates. These are reckoned as 

 peractinal plates. They correspond in number and size with the 

 marginals and are placed close to the adambulacrals, which they join 

 generally with no connecting ossicles between; when rarely such 

 ossicles occur, they are few and very small or rudimentary. In the 

 narrow channel between the peractinal and adambulacral plates 

 there is a row of small papular areas, each with one or few rounded 

 papulae. Each peractinal plate bears two strong equal spines, 

 decidedly larger and longer than the marginals, the proximal ones 

 2 mm. to 3 mm. long. Their tips are usually flattened, and often 

 enlarged and fluted or grooved. 



The adambulacral spines are numerous and regular, two to a plate, 

 forming two close rows ; they are tapered, blunt or subacute, about 

 four pairs corresponding to one peractinal plate. Major pedicellariae 

 are few on the type. Those found were on the adambulacral spines 

 and inner margins of their plates. They are rather large, lanceolate, 

 acute, about as thick as the adjacent spines. None were found on 

 the back. 



The disk is reticulated much like the rays, with large angular 

 interspaces. The madreporite is large (5 mm.), prominent, with 

 radiating and dichotomous gyri. It is surrounded, in the type, by 

 seven spines, like the other adjacent spines. 



The central disk-spine rises from a five-lobed plate. It is sur- 

 rounded by five spines, and beyond this with a circle of ten spines. 



The type is from Departure Bay, Nanaimo, British Columbia, 

 twenty-five fathoms, mud (Chas. H. Young, Canadian Geological 

 Survey, 1909). 



This species seems to be closely related to the genus Orthas- 

 terias, in several respects, and especially to 0. kcehleri, by reason of 

 the rather indefinite or sublongitudinal arrangement of its dorsal 

 spines, in about seven obscure rows. It differs from the latter in 

 the shorter, stouter, fluted and crowded dorsal spines ; the prominent 

 median row ; the double peractinal row of elongated spines ; etc. 



