50 VERRILL 



aa. Only three regular rows of dorsal plates with spines. 



Stylasterias Ver., nov. Type, 5". forreri (Lor.), 

 aaa. Usually only one row of dorsal plates (median) developed; they are 

 broad, covered with a thick channeled dermis. 

 Sclerasterias Per. Type, S. guernei Per. E. Atlantic. 

 DD. One row of interactinal plates without or with spines (monactinoplacid). 

 Three to five or more rows of dorsal plates and spines. Major 

 pediceliarise of two kinds. Some compressed, lanceolate or ovate; 

 others large, thick, spatulate or wedge-shaped. Rays five or six. 

 Orthasterias Ver., nov. Type, O. colnmhiana Ver., nov. 



ii. two or more rows of actinal plates and spines 

 (polyactinoplacid) . 



A. Diplacanthid. Special large dermal pedicellarias are unguiculate or feli- 



pedal. 

 a. Spines vesiculated. 



Cosmasterias Sla. C. tomidata (Sla.). 

 aa. Spines not vesiculated. 



Cosmasterias lurida (Phil.) = sulcifera Per. 



F. SUBDIVISIONS OF ASTERIIN^ WITH RETICULATED DORSAL 



SKELETONS. 



This large group presents fewer morphological characters for gen- 

 eric and subgeneric distinctions than the last, and some of them 

 present gradations and intermediate conditions. However, if we 

 separate the genus Pisaster and consider the large group to which 

 Asterias rubens, A. vulgaris, and A. forbesi belong as typical 

 Asterias, there will be left several more or less differentiated types of 

 structure. 



Genus Leptasterias Verrill. 



Type, L. miilleri (Sars.). 



This group, as separated by me, 1866, differs from true Asterias 

 plainly in having only a few large papulae in each cluster. Its 

 typical species are L. miilleri, L. compta, L. tenera, etc. In these 

 the dorsal spines are slender and numerous and the interactinal spines 

 are in one row (rarely two). The discovery of numerous additional 

 species, of larger size, and having more papulae, now renders it diffi- 

 cult to make any sharp distinction, in this respect, between the two 

 groups. Hence I have sometimes considered it as of only subgeneric 

 value, and closely connected with typical Asterias. Its typical species 

 carry the large eggs and young attached to the oral region, and the 

 development is direct or abbreviated. 



