ASTEBOIDEA OF NORTH PACIFIC AND ADJACENT WATERS — FISHER. 199 



short, stout, truncate, slightly tapering, spiniform jaws. On the distal part of 

 the ray one or two of the spineiets on the central part of the plate become con- 

 siderably longer and thicker than the rest. 



Mouth plates, rather small and not prominent actinally, with a furrow series 

 of five to seven i)rismatic compressed spineiets (the innermost largest and most 

 compressed) and a parallel actinal series of three to five thicker prism.atic spineiets 

 all similar to but larger than the adambulacral spineiets; outer part of plates with 

 granules. 



Color in life, abactinal surface deep brilliant poppy red to vermilion; actinal 

 surface "salmon" orange; tube feet scarlet with sucking disks of flesh color. 



Anatomical notes. — Abactinal plates, when viewed from the inner surface, are 

 rather small and roundish with short blunt lobes, wiilely separated in fully grown 

 specimens, and connected by radiating independent ossicles. (See fig. 1, pi. 59.) 

 These ossicles leave triangular papular spaces in which two or three papulte com- 

 monly occur. The papular area is very extensive, comprising practically all the 

 abactinal surface except the very restricted interradial areas (where the plates are 

 close together and lack ossicles) and a small space at the tip of ray. The papular 

 area is more extensive, especially interradially, than in M. bairdii, M. ornatus, or 

 M. arcuatus, all of which possess the internal radiating ossicles. 



I was considerabh' sui-prised to find rudimentary superambulacral plates in 

 this species. Mediaster bairdii, M. aj-cuatus, and M. ornatus were examined and 

 found to possess them also. Ceramaster lacks any trace of the plates, as does also 

 NympJiaster fcrnalis and Nereidasfer bowersi. I think it probable that all species 

 of Mediaster have rudimentary superambulacrals. In M. sequalis they begin with 

 the second ambulacral ossicle and extend far along raj-, or until the lower end of 

 ambulacral ossicles touch the inferomarginals. The plates are small and oval in 

 form (PI. 59, fig. Ic), are entirely covered by connective tissue, so that the skeleton 

 must be treated with caustic potash before they can be seen. In M. arcuatus 

 (Sladen), 21. bairdii (Verrill), and 31. ornatus Fisher the ossicles do not begin so 

 near the mouth, but start at varying distances therefrom, and tlie out under the 

 same conditions as in sequalis. In .V. arcuatus the plates are slender and longer 

 than in any other species. 



The actinal intermediate plates, from the internal view, are broadly oval and 

 slightly imbricated. 



Intestinal coccum consisting of five irregular, unequal, sparsely lobed divisions, 

 the longest reaching to margin; no central portion, the divisions meeting at the 

 intestine; anus present; hepatic cccca long; stomach small. Gonail in three tufts 

 on either side of the uncalcified inteiradial septa. Tube feet with sucking disks. 



Variations. — When compared with specimens from Chignik Bay. Alaskan 

 Peninsula, Southern Californian examples present no greater differences than such 

 as result from individual variation. Xorthern specimens appear to be better sup- 

 plied with pedicellaricT, especially uii the distal adambulacral plates, but even in 

 this respect Chignik Bay examples vary somewhat. 



Among the Calift)rnian specimens the most important differences are due to 

 age. The small examples have more prominent marginal plates than the medium- 

 sized and large examples, and much fewer pedicellaria\ these being absent from 

 the distal adand)ulacral plates. Th" ndambulacial pedicellariir are rare in Cali- 



