164 bulletin: museum of comparative zoology. 



armature, easily recognized. The marginal and usually also some of 

 the adjacent suboral spines form a prominent angular cluster at the 

 mouth of the furrow and to the side of the enlarged tooth, the apex 

 being nearer the peristome than is the base of the latter. That is, 

 the marginal series bends downward deep in the furrow and then 

 remounts to the base of the tooth. In Blakiaster there is a slight 

 hint of this, but the series is not at all strongly angular and does not 

 form a cluster deep in the furrow. The suboral armature is similar 

 in the two groups. 



An important difference between the two genera is the abactinal 

 skeleton. In Persephonaster the plates are independent, low, flat- 

 topped paxillae, hexagonal to lozenge-shaped, and sometimes with 

 slight indication of lobing. In Blakiaster the skeleton consists of 

 strongly lobed, overlapping, low convex plates simulating tabulate 

 paxillae. The actinal intermediate plates in typical Persephonaster 

 extend farther along the ray and often bear an enlarged specialized 

 spine, and the odd interradial actinals of Blakiaster are never present. 



The resemblance of Blakiaster to Leptychaster is in the armature 

 of the adambulacral, mouth, ami actinal intermediate plates, but the 

 resemblance is no closer than that existing between Leptychaster 

 pacificus or L. anomalus and Persephonaster. Leptychaster like 

 Blakiaster has a row of odd interradial actinal intermediate plates. 

 The abactinal and marginal plates of Leptychaster are wholly unlike 

 those of Blakiaster. If Blakiaster really lacks an intestinal coecum, 

 which I am inclined to doubt, the genus will be sharply set off from 

 other Astropectinidae. 



The genus Bunodaster, very briefly diagnosed by Verrill (Amer. 

 nat., 1909, 43, p. 554, fig. 4), seems to be identical with Blakiaster. 

 Professor Verrill has kindly furnished me with enlarged photographs 

 of the type, B. ritteri. The abactinal plates, described by Verrill as 

 pseudopaxillae, are, superficially at least, like those of Blakiaster. 

 The same is true of the marginal and actinal plates with their armature. 

 The actinal intermediate plates are similar in distribution and the 

 second and third series each has the odd interradial plate precisely 

 as in Blakiaster. I can find no differences in the adambulacral and 

 mouth plates. 



