REPORT ON THE ECHINOIDEA. 201 



showing that the lateral fasciole is an extension of the anal fasciole, and that as far as we 

 know the lateral and anal fascioles, when they appear independently or united, are of 

 greater permanence than when the anal fasciole appears as a branch of the subanal fasciole. 

 These young Schizasteridaj show very plainly that such genera as Acestc are strictly 

 embryonic Schizasteridse ; that is, they retain as the young of Schizaster very rudimentary 

 posterior lateral ambulacral petals, the odd anterior ambulacrum occupies the greater part 

 of the abactinal surface of the test, the ambulacral suckers of this odd ambulacrum retain 

 the gigantic size for which they are marked in the younger stages, and the peripetalous 

 fasciole follows closely the lines di-awn from the extremities of the petals. At a stdl earlier 

 stage when Schizaster is more globular, it assumes a still more embryonic stage as the 

 young of Brissojysis, that is, it passes then through what might be called its Hemiaster 

 stage, and of this stage, when the actinostome is as yet not developed, Aerope is the 

 representative at the present day ; having the prominent peripetalous fasciole, the greatly 

 developed odd anterior ambulacrum, but slightly sunken at first in the Aceste stage, and 

 scarcely flush with the test in the Hemiaster stage, with its gigantic ambulacral suckers, 

 and the more or less cylindrical shape so characteristic of all young Spatangoids. To a 

 certain extent Agassizia may be regarded also as an embryonic type ; it retains the 

 globular shape of young Spatangoids, and the structure of the petals is embryonic in part. 

 The presence of a well developed lateral fasciole dates back to the cretaceous Prenaster. 

 The unsatisfactory nature of the characters derived from the extent and course of the 

 lateral fasciole is well showTi from the subdivisions of Faorina attempted by Troschel, 

 which are based mainly on the fascioles. Although the presence of a peripetalous fasciole 

 appears greatly to modify the character of the abactinal part of the ambulacra, yet we are 

 not able to make any classification of the Spatangoids based on the presence or absence of 

 fascioles alone which corresponds in any way to the other structural afiinities. The 

 Prymnodesmians of Loven (Spatangoids with a subanal fasciole) unite such widely distant 

 types as Palceotroinis, Spatangus, Brissus, and Breynia ; while among the Prymnadetes 

 we find Hemiaster, Desoria, and Schizaster, and it is often very difficult, as in the case of 

 Urechinus and many fossil genera, to decide whether they belong to the Adetes or either 

 of the other groups, and we find in the Pourtalesise, for instance, otherwise closely allied 

 genera which would in this character alone he i^laced either in the one group or the 

 other. 



Schizaster fragilis. 



Brissus fragilis, Diib. o. Kor., 1844, Skand. EcHn., p. 280. 

 Schizaster fragilis, Agassiz., 1847, C. R. Ann. Sc. Nat., vol viii. p. 22. 



The Challenger collected this species ofl" the coast of Nova Scotia. It has also been 

 dredged by the United States Fish Commission in the Gulf of Maine. This species like 

 Brissoixsis lyrifera and S2X(taiigus raschi, has an extensive geographical range in the 



(ZOOL. CHALL. EXP. — PART IX. — 1881.) I 26 



