DESCRIPTIONS OP THE SPECIES. 271 



the anal interradius are more or less abortive ; sinuses wide and deep, generally with 



relatively steep sides. Deltoid plates small, and confined to the summit, where they 

 are either horizontally placed or inclined inwards. Lancet-plates concealed by the 

 side plates (in all but one species) ; outer side plates very small. Spiracles rarely 

 present. Ten groups of hydrospires, which are pendent, and open externally by a series 

 of elongated slits with intervening ridges, distributed in Bubparallel scries on the 

 sloping- sides of all the radial sinuses. They are only partially covered by the 

 ambulacral plates, their distal ends (or even the entire length of some) being visible 

 on the sides of the sinuses. Column large as compared with the size of the calyx. 



History. We established the genus Pkamoschisma in 18S2 for a small number of 

 interesting species previously included in Pentremites. The late Mr. E. Billings, in 

 a remarkable article " On the Structure of the Crinoidea, Cystidea, and Blastoidea," l 

 referred as follows to the peculiar characters of Pentri mites caryophyllatus, de Koninck 

 (PI. XIV. figs. 3, 4) : — " The ends of the fissures of the hydrospires are seen along 

 the sides of the angular ridges, which extend from the apices of the pyramids to the 

 angles between the arms. T do not think that such species can be referred to Pen- 

 tremites; and if I had specimens before me instead of figures only, I would most 

 probably institute a new genus for their reception." As we entirely agree with 

 Mr. Billings's remarks, it has afforded us much pleasure to adopt and extend his 

 suggestion by proposing the name Pkamoschisma for Blastoids possessing these 

 characters. 



Remarks. The appearance of some (often many) of the hydrospirc-slits externally 

 is a very striking feature in Phcenoschisma and distinguishes its species at once from 

 the other Blastoids which they may resemble in external form. Thus, for example, 

 P. Archiaci and some species of Pentremitidea are not at all unlike in side view 

 (PL IV. fig. 11 ; PI. XII. fig. 10 ; PI. XIV. fig. 13). But the summit-characters of 

 the former type (PI. XIV. figs. 5-7) are altogether different from those of the Pen- 

 tremitidce, and indicate its relationship to Codaster. The same may be said of 

 P. caryophyllatum (PI. XIV. figs. 1-4), entire examples of which might readily be 

 mistaken for aberrant forms of Pentremites, as is well seen in Roemer's figure 2 . No 

 one, however, could possibly say this of P. nobile or of P. Verneuili (PL XI. figs. 1-6), 

 types that are obviously very closely allied to those species of Codaster (PL X. 

 figs. 19, 20 ; PL XII. figs. 1-6) which have the radial sinuses more deeply excavated 

 than is the case in the British C. trilobatus (PL XIII. figs. 1-4). 



The presence of hydrospires in the anal interradius sharply distinguishes Phceno- 

 schisma from Codaster, and so renders the former a less aberrant type than it would 

 otherwise be (PI. XI. fig. 6 ; PL XIV. figs. 5, 11). Its deltoid plates are limited to 



1 American Journ. Sci. 1S00, vol. xlviii. p. SO ; Canad. Nat. & Geol. 1869, voL iv. p. 288; Ann. & Mag. 

 Nat. Hist. Wo, vol. v. p. 262. 



2 Archiv f. Xaturgesch. 1851, Jahrg. xvii. Bd. i. Taf. iv. f. 10. 



