362 SMITHSONIAN MISCELLANEOUS COLLECTIONS [ V '0L. 50 



short joints, slender, tapering, and almost flagellate; following pin- 

 nules with 3 to 5 of the joints much expanded laterally, enclosing 

 the genital glands, which are covered with strong protecting plates ; 

 remaining pinnules prismatic; all the pinnules, especially the lower, 

 have the first joint much wider than its successors. 



Color in life, yellow when young, becoming when adult dull, 

 yellow-brown or dark gray-brown. 



Type of the genus. — Antedon acoela P. H. Carpenter, 1888. 



Pcecilomctra is closely related to Charitometra, but it appears to 

 be an invariably ten-armed type. The costals are peculiar in pos- 

 sessing a thin border, continuous laterally and posteriorly, and in 

 having the sides more or less strongly concave, characters which 

 appear to warrant generic differentiation. The range of Pcecilo- 

 mctra is from the Meangis Islands north to southern Japan. Two 

 species are known, but the differences between them are not great, 

 and it may be found necessary to unite them at some future time. 

 The later species was wrongly described as belonging to Dr. Car- 

 penter's "Basicurva group," the author having been misled by the 

 association in the same group of Pcecilomctra acoela and Calometra 

 discoidea, two widely different forms. The error is, however, quite 

 inexcusable. The two species of this genus are: 



Pcecilometra acoela (P. H. Carpenter) Poecilometra scalaris (A. H. Clark) 



17. CALOMETRA, gen. nov. 



Centro-dorsal discoidal, bearing 15 to 20 cirri in a single, or par- 

 tially double or triple, more or less definite marginal row ; cirri 

 rather stout, with 20 to 50 segments, the more proximal more or 

 less elongated (but never very much so), the distal very short, 

 usually with small, blunt dorsal spines ; disk completely covered with 

 calcareous plates ; pinnule and brachial ambulacra well plated ; 

 costals rounded, widely free laterally, or furnished with lateral (but 

 not posterior) marginal flanges meeting the flanges on the adjacent 

 rays; distichals (when present) two; palmars two (rarely one), 

 usually articulated, but sometimes united by syzygy ; ten to fifty 

 arms of moderate length, rather stout, evenly tapering, the brachials 

 triangular or very obliquely quadrate, almost always longer than 

 wide, convex on the longer edge, becoming shorter distally; position 

 of syzygia irregular; lower pinnules with the first two joints (espe- 

 cially the first) greatly expanded, this character most marked on 

 the first pinnule, which is always small and weak, with small, squar- 



