SHALLOW-WATER STARFISHES 329 



Dorsal ossicles either paxilliform, or simple plates with a single 

 spinule. Interactinal plates flattened, imbricated. Adambulacral 

 armature simple, uniserial. Ampullae single. No intestine. Dorsal 

 pore generally absent. Superambulacral plates usually absent. 



The stomach is very large; the food consists of fine mud or sand 

 containing foraminifera, etc., which these starfishes swallow in large 

 quantities. Hence they are best adapted to life on bottoms of " Glo- 

 bigerina ooze," in the deep seas. 



This family was divided by Sladen, 1886, into two subfamilies: 

 Porcellasterinae and Ctenodiscinae. 



PORCELLASTERINyE Sladen. 



In these there are special localized cribriform organs. No fascio- 

 lated channels between the interactinal plates. Superambulacrals 

 always or nearly always lacking. All are confined to deep water. 



CTENODISCIN^: Sladen. 



In these there are simple fasciolated channels between the inter- 

 actinal plates and continuous with more definite ones between the 

 marginals, covered by small, flat spinules. (See pi. v, figs. 6-8a.) 

 Dorsal plates are paxilliform. Superambulacrals are present. 



Subfamily CTENOD1SCIN& Sladen. 



Ctenodiscina (subfamily of Porcellanasterida') SLADEN, op. cit., 1886; Voy. 

 Chall., xxx, pp. 127, 170, 1889. 



Disk broad, flat, with short rays. Marginal plates thin, covered 

 with membrane, not granulose, paired and conterminal, in two 

 closely united rows, furnished laterally with specialized fasciolate 

 grooves, covered by a single row of flattened spinelets. Disk usually 

 with true paxillae; paxillar columns enlarged at base, but isolated. 

 Actinal interradial areas covered with flat plates, with fasciolated 

 grooves between the rows or double rows, continuous with those 

 between the marginal plates and adambulacral plates. 



An unpaired interradial marginal plate, in each series, is present 

 in Pectinodiscus Ludwig ; also an odd row of actinal plates. 



Adambulacral plates with a divergent group of furrow-spines, and 

 some on the actinal side. A minute central dorsal pore, often on an 

 elevation. 



At present this subfamily includes only Ctenodiscus and Pectino- 

 discus Ludwig. It is nearly intermediate in many respects between 



