108 



DESCPJPTIOX OF THE HAED PAETS OF SOME 



vertical plates rising close to the actinal ring from the interbrachial in- 

 terambulacral plate. 



Fig, 4.* FiS- 5.t 



This species of Asteropsis occurs on the West Coast, from Vancouver's 

 Island to San Francisco. 



The general arrangement of the limestone plates of the European As- 

 teropsis pulvillus does not differ materially from the one here figured. 

 The European species carries spines on the edge of the marginal as 

 well as of the interambulacral plates, and the interbrachial arch is more 

 fully developed, separating adjoining arms more completely. 



Pentaceros reticulatus. 



Pentaceros reticulatus Linck, 1733. De Stellis Marinis. 



PI XVI 



Figs. 1, 2, 4, 5, on PI. XVI., show the extent to which the lime- 

 stone network of the actinal and abactinal surfaces is hidden by the 

 spines and granules covering the plates and rods of the two surfaces. 

 Seen from the abactinal side, the network consists of a central plate 

 more or less hexagonsd, with projecting angles connected together by 

 short stout rods, overlapped by the plates, so as to form an open tri- 

 au'^ilar network, covered by minute granules, and in their interstices 

 giving passage to the thickly clustered water-tubes (PI. XVI. Fig. 1). 

 The same granulation covers the plates and rods as well as the greater 



• /•'(>/. 4 is an interior view of the aotin.il plates of a Cnlcita, as seen in an alcoholic si>ecimcn, of 

 whirh the abactinal floor h:is been removed to show the intricate system of passages lying between the 

 limestone rods, a /*, aliactinal system; s, section across a limestone rod; /", interior muscular sheath con- 

 necting limestone nxls; o, passages K'tween adjoining plates. 



f FkI- .'», edge of a C»d<-ita, to show the gradual passage of the open reticulation of the aKictinal 

 surface into the closely packed vertical wedges hi j\ forming the outer edge of the disk of a Culcita. 



