194 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Mouth plates with about 8 marginal spines, the inner two con- 

 siderably enlarged. One prominent suboral spine is present near 

 the inner end of the plate, and a series of about 7 or 8 spinelets 

 follows the margin of median suture. Several spinelets are present 

 on the outer part of the plate between the adambulacral margin and 

 median suture. The enlarged subambulacral is sometimes absent, 

 or poorly developed (station 5619, small specimens). 



Pedicellariae are present: (1) Rarely on the vertical (interradial) 

 suture between the first superomarginal plates of either ray (station 

 5619) ; (2) in a similar position on the inferomarginals (same 2 

 specimens, but not in all interradii) ; (3) fasciculate pedicellariae 

 on a variable number of inferomarginals beyond the second or third, 

 and near inner edge of plate. There are 8 to 12 on either side of 

 the ray in the largest specimen, and sometimes 1 or 2 spinelets be- 

 long to an adjacent adambulacral plate. Each pedicellaria, which 

 is circular, is composed of 5 to 7 sharp spinelets. These pedicellariae 

 are lacking on small specimens from stations 5626 and 5658, and few 

 on a specimen from stations 5624, 5618, and 5445. (4) Two or 3 

 pectinate pedicellariae (sometimes as many as 6) are present in each 

 interradial area. Rarely a pedicellaria is fasciculate and confined 

 to 1 plate (stations 5147, 5619). 



A small specimen from station 5658 and 2 from station 5348 (the 

 largest having R equal to 21 mm.) lack pedicellariae. There are 14 

 adambulacrals to the first 10 inferomarginals, and at most only 2 

 papular pores to each papularium. These specimens are placed here 

 rather than under Pectinaster hylacanthus because the superomar- 

 ginal plates encroach conspicuously upon the abactinal surface and 

 the superomarginal spines are situated near the outer part of the 

 plate. In P. hylacanthus the superomarginals are confined to the 

 side of the raj^ The specimens are classed with niasicus rather than 

 with Ch. inops on account of the more numerous abactinal spines. 

 They may really be small examples of Ch. pilosus Alcock. It is not 

 possible, as a rule, to be entirely certain of the identification of 

 young Cheiraster and Pectinaster. The specimens just mentioned 

 do not e«hibit any characteristics which would place them unequivo- 

 cally in either genus, and without the adults for comparison it would 

 not be possible to say whether they belong to Pectinaster or Cheir- 

 aster. As to the specific identification, it must be considered only 

 as probable. Cheiraster pilosics, Ch. inops, and Ch. niasicus are very 

 closely related. I am not certain of the characters of Ch. pilosus. 

 Alcock describes and figures several accessory inferomarginal spines, 

 while Ludwig (1910, p. 456) writes that there is only 1 (in contra- 

 distinction to inops and niasicus, which have several). Alcock fig- 

 ures and not very definitely describes actinal intermediate pedi- 

 cellariae, indicated also by Ludwig (1910). Koehler (1909, p. 13) 



