REPORT ON THE ASTEROIDEA. 585 



that their presence is in relation to the encircling wreath of forcipiform pedicellarioe at the 

 base of the spines. 



The adambulacral plates are very small, and their armature consists of a single short, 

 delicate, tapering spinelet about l - 5 mm. long, or a trifle more, the series of which forms a 

 regular longitudinal line on each side of the furrow. At the base of these spines and quite 

 within the furrow is an irregular and often interrupted series of small forficiform pedicel 

 lariae, generally more or less pedunculated. 



The ambulacral furrows are wide, and the tube-feet, which have a very small, button- 

 like terminal disk, are biserial in arrangement at the base and on the outer part of the 

 ray, but are crowded and assume an alternating quadriserial arrangement about the middle 

 of the ray. 



The actinostome is very wide, measuring about 11 mm. in diameter, and there is a 

 broad exposed buccal membrane. 



The madreporiform body, which is rather small and inconspicuous, is situated nearer 

 the margin than midway between the centre and the margin, and its surface is marked 

 with fine convoluted striations. 



The anal aperture is large and excentric in position. 



Colour in alcohol, a bleached ashy white. 



Locality. — Near Zebu, Philippine Islands. January 19, 1875. Depth 95 fathoms. 



Remarks. — The resemblance of this form to Brisinga at first glance is very striking. 

 The small, well-defined, button-like disk, the long narrow and easily detachable rays, the 

 simplicity of the skeletal framework, and the widely expanded actinostome at once recall 

 that group of starfishes. On the other hand, the structural affinities of Asterias (Stolas- 

 terias) volsellata clearly point in the direction of Asterias (Stolasterias) tenuispina, 

 Asterias (Stolasterias) calamaria, and their allies, and although there is much tempta- 

 tion to recognise the striking features of the external form above referred to by placing 

 the species in a distinct genus, I do not after careful study feel justified in taking this step 

 on the strength of the single example at my disposal. 



Although I am quite disposed to think that the group of species of which Asterias 

 tenuispina is the type will ultimately be separated as an independent genus, which may 

 well be called Stolasterias, I prefer at present to treat them as I have done other groups 

 considered in this Eeport, and to rank them provisionally only as a subgenus, until more 

 is known of the anatomy of the various constituents of the present genus Asterias, and 

 the partition can be undertaken on a sounder and more definite basis than is yet possible. 



Apart altogether from these considerations, Asterias (Stolasterias) volsellata furnishes 

 a highly interesting link between the Asteriidse and Brisingidse, and shows that the two 

 families are not so widely separated as they were at one time considered to be. I am 

 inclined to think that the Brisingidse are the degenerate descendants of a not very remote 

 ancestor, modified through the action of complete isolation. 



(ZOOL. CHALL. EXP. — PART LI. — 1888.) 74 



