ECHNIOIDEA. II. 



43 



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 subanal fascicle; 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 subanal region, which is seen invariably with a true subanal fascicle. It may be that 

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

 allied, as in the instance of Micraster and Epiaster; or the fascicle ma}' 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 

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

 distinct from those without a fascicle. -- 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 commonly 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 -j- x, 

 present in all Prymnodesmic Spatangidse. Its deficiency in Urechinus is a sure sigh 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- 

 neously Agassiz in the Blake-Echini p. 52 states that the structure of the subanal fascicle in Ur- 

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

 .... and a stage in which the fascicle is indicated merely by irregular accumulations of miliary tu- 

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

 subanal fascicle (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 fascicle 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 pedicellarise on them. There can, however, scarcely be any doubt that they are 

 really U. naresiantts. 



6* 



