ECHNIOIDEA. II. 



43 



St. 18 (61° 44' Lat. N. 30° 29' Long. W. 1136 fathoms 3°oC.Bottom temp.) 23 spec. 



— ) 27 - 



— ) 39 — 



— II' — 



— ) !■ - 



— ) I — 



— ) 3 - 



The species was hitherto recorded onl\- from the dredgings of the Challenger , Blake and 

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

 (loc. cit.) has throwu doubt 011 their being all really U. iiaresianus. «It must be admitted that the shape 



and details of U. iVarcsi gi\-en in the v 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), withont the peculiar arrangement of the pores of the postero-lateral am- 

 bulacra in the subanal region, wliich is seen invariably with a true snbanal fasciole. It ma\' be that 

 there are two groups of forms, one withont and the other with a subanal fasciole, and \et closelv 

 allied, as in the instance of Micraster and Epiastcr; or the fasciole mav 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 witli a distinct fasciole are specificalh' 

 distinct from those withont a fasciole. — Loven (On Pourtalesia. p. 91) points out that the ambulacral 

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

 offered by the corresponding piates of the posterior interradium, a structure conimonly met with also 

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

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

 present in all Prymnodesmic Spatangidæ. 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 accumnlation of ordinar\- miliar\- 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 'fa.sciole in Ur- 

 cclii)ins assumes all the stages of development intermediate between a well defined subanal plastron 

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

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



subanal fasciole (the onh- one existing) is still in process of formation . 



Though Duncan thus reserves the final .solution of these questions for Profes.sor Agassiz, I 

 niay be allowed to set forth a few remarks thereon. I must fnlly 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 \onng 



I 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 httle 

 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 ain- globiferous pedicellariæ on them. There can, however, scarcely be any doubt that they are 

 reallv U. naresianus. 



