ECHNIOIDEA. II. 43 



) 27 



I 39 — 

 ) i 1 - 

 ) i 1 - 

 ) 1 - 

 ) 3 



The species was hitherto recorded only from the dredgings of the Challenger , Blake and 

 the Cape investigations (Bell. Op. cit). Regarding the specimens from the Challenger Duncan 

 (loc. cit.) has thrown doubt on their being all really U.naresianus. «It must be admitted that the shape 

 and details of U.Naresi .... given in the Challenger-: Report, PI. XXIX, XXX, XXX a. are not those 

 of one species. Some forms have and others have not a snbanal fasciole; and these last are, moreover, 

 (as Loven has pointed out), without the peculiar arrangement of the pores of the postero-lateral am- 

 bulacra in the snbanal region, which is seen invariably with a true subanal fasciole. It may be that 

 there are two groups of forms, one without and the other with a subanal fasciole, and yet closely 

 allied, as in the instance of Mic raster and Epiastcr; or the fasciole may be so small in the area which 

 it surrounds, that it does not interfere with the ambulacra. The final solution of these questions must 

 be left to the distinguished author of the Report on the Challenger -Echini . - - Also Lambert 

 (Echinocorvs. p. 29. Note) is of opinion that the specimens with a distinct fasciole are specifically 

 distinct from those without a fasciole. — Loven (On Pourtalesia. p. 91) points out that the ambulacral 

 plates I. a. 4 and V. b. 4 are slightly expanded interiorly, so as to fill up the feeble re-entering angle 

 offered by the corresponding plates of the posterior interradium, a structure coraraonh met with also 

 in Holaster and other Meridosterni, and in the Prymnadetes, that is, in forms devoid of a subanal 

 fasciola, and in no wise to be compared with the well known wedge-shaped, extended plates 6 + x, 

 present in all Prymnodesmie Spatangidae. Its deficiency in Urechinus is a sure sign of the absence of 

 a subanal fasciola, of which not one of the several specimens carefully examined showed the least 

 trace. There is, close under the periproct, a dense accumulation of ordinary miliary tubercles, not un- 

 like that seen in the same position in some Brissi; it has no relation to the fasciola . — Contempora- 

 neouslv Agassiz in the Blake -Echini p. 52 states that the structure of the subanal fasciole in Ur- 

 echinus assumes all the stages of development intermediate between a well defined subanal plastron 

 .... and a stage in which the fasciole is indicated merely by irregular accumulations of miliar} tu- 

 bercles. So that the genus Urechinus is the representative of the oldest Spatangoids in which the 



subanal fasciole (the only one existing) is still in process of formation*. 



Though Duncan thus reserves the final solution of these questions for Professor Agassiz, I 

 may be allowed to set forth a few remarks thereon. I must fully join Professor Agassiz in his state- 

 ment about the fasciole; I likewise find all transitional stages between a distinct fasciole and no 

 traces at all of a fasciole, even in specimens from the same locality. Moreover, I find that in young 



1 The two specimens from St. 39 and 40 differ somewhat in shape from the other specimens, the- test being lower 

 and more regularly rounded. The peristome is somewhat smaller than usual, and the secondary tubercles perhaps a little 

 more prominent and numerous. Otherwise I do not find any difference. Unfortunately they are both almost denuded so that 

 I have been unable to find any globiferous pedicellariae on them. There can, however, scarcely be any doubt that they are 

 really U. naresianus. 



6* 



