1888.] 



NATURAL SCIENCES OF PHILADELPHIA. 



421 



ON TWO NEW SPECIES OF STARFISHES. 



BY J. E. IVES. 



While engaged in reviewing the starfishes in the collection of the 

 Academy, I found two forms belonging to the genera Pteraster and 

 Coronaster which do not appear to have been described. They may 

 be thus characterized: 



Pteraster tesselatus, n. sp. , 



Dorsal surface very convex : arms tapering at their aboral ends, 

 and much recurved. Rupradorsal membrane regularly reticulated ; 

 reticulation forming obliquely arranged hexagonal areas, which are 

 very apparent upon the sides of the arms. No spicules found in the 

 supra-dorsal membrane. Paxillse about 2 mm. high. Each paxil- 

 la surmounted by eight radiating spinelets enclosing a number of 

 .smaller ones. 



The spinelets when examined under the mi- 

 croscope are found to be composed of two or more 

 connected many-sided hollow^ cylinders, the sides of 

 which are perforated by elongated apertures as shown 

 in the figure representing a portion of a cylinder 

 highly magnified. The distal ends of the spinelets 

 are inserted into the delicate membranous bands which 

 form the reticulation of the supra-dorsal membrane. 

 Some of the spinelets perforate this membrane in the 

 centres of the hexagonal areas, projecting slightly on 

 the surface. On the dorsal surface of the disk and arms, especially 

 in the hollows of the inter- radial portions of the disk and of the 

 recurved arm, there are numerous minute folds of the integument 

 that produce a somewhat granulate appearance of the membrane. 

 There are 25-30 spiracula in each hexagonal area. The oscular 

 orifice is surrounded by a number of webbed spinelets. 



On the ventral surfiice the actino-lateral spines are short, about 

 70 on each side of the ambulacra! furrow. There are a correspond- 

 ing number of ambulacral combs. At the base of the arm each 

 comb has 6 spines ; the three outer spines are the longest and about 

 equal ; the fourth (counting from the outside) rather smaller, the 

 fifth very small, and the rudimentary sixth spine very minute, and 

 directed towards the aboral end of the arm. The number of spines 





