FIBULARIA VOLVA. 509 



developed in this species than in any other of the genus, although, both in 

 this species and in F. volva, no trace whatever of the rudimentary anal 

 radiating partitions existing in Fibularia australis exists. In this species the 

 pores of older specimens are very indistinctly conjugate. 



Indian Ocean ; Philippine Islands. 



Fibularia volva 



I Fibularia volva Agass., 184 7, C. R. Ann. Sc. Nat., VII. p. 142. 



This species is elongate, pointed at both extremities, flattened from above, 

 regularly arched ; edge of test rounded ; mouth slightly posterior ; anus very 

 small, placed close to the mouth ; actinal side convex, re-entering towards 

 the actinostome ; ridges of the median part of interambulacra prominent 

 on the lower side, near the anterior extremity , indistinct on the abactinal 

 side. In one of the specimens examined the buccal and anal membranes 

 were still preserved, and on opening the specimen very minute and delicate 

 jaws could be seen, though the auricles were highly developed, — fully as 

 well as in Echinocyamus. To the homology of the auricles I will return 

 again when speaking of the Cassiduloids proper, to show that it is by no 

 means safe to ascribe jaws to Clypeastroid genera from the presence of 

 auricles alone, even when apparently well developed. 



The tubercles of this species are large, distant on the abactinal side, but 

 closely packed together on the actinal side ; as they approach the actino- 

 stome the miliaries are larger and more prominent than in other species. 

 The diverging petals are formed of from four to six large distant pairs of 

 pores ; the poriferous zones are continued by isolated distant pores to the 

 actinal side close to the actinostome. The actinostome is covered, as in 

 Echinoneus, with a membrane stiffened by minute calcareous plates, ar- 

 ranged concentrically round the central opening of the mouth ; the actino- 

 stome is not central, it is placed somewhat nearer the posterior edge. 



Red Sea ; Formosa ; North Australia. 



