164 SYNOPTIC COLLECTION. 



and their openings are also seen in this preparation. No. 

 296 shows the stomach and its coecal appendages. 



The marginal plates in these forms are large, but those 

 on the upper side have become small in Pentaceros 

 modestus Gray (No. 297). The interambulacral plates are 

 of good size and the tube feet have large suckers. The 

 aboral disc and the sides of the arms are provided with 

 stout conical spines. 



This tendency for the large marginal plates of the 

 primitive forms to become reduced in size is seen in 

 Paulia horrida Gray (No. 298). The spines in this 

 genus are large and strong, and are found on the most 

 exposed points. 



In the starfishes so far described the development of 

 the ambulacral system and of the test or skeleton goes 

 on together, but in the more specialized forms which 

 follow, the development of the ambulacral system is 

 accelerated. 1 



In Linckia unifascialis Gray (No. 299) the disc is 

 small and the arms long and six in number. Like the 

 earlier forms it is spineless. The marginal plates are 

 reduced in size. The ambulacra are narrow and some- 

 what crowded, while they carry two rows of tube feet 

 provided with suckers. The tendency to multiply the 

 number of arms is seen in Solaster endeca Forbes (No. 

 300). Here there are nine rays radiating from a disc of 

 considerable size. There are few spines, and the surface 

 is granular. The two rows of ambulacral feet are pro- 

 vided with sucking discs. 



The deep-sea species, Zoroaster fulgens Wyv. Thorn. 

 (PI. 301, figs. 1-3), is of especial interest. The young 

 (fig. i) has a much higher disc than the adult. The 

 plates of the aboral side are distinctly seen, and for this 

 reason the genus is an admirable one for comparison 

 with Crinoids. The central plate is surrounded by five 



1 Sladen, Chall. Rep., Zool., XXX, part 51, 1889, p. xxxv. 



