KCHINOIDKA. II. 



69 



It seems very doubtful, as pointed out by d'Arcy Tlionipsou (Op. cit.) whether tlie specimen 

 described and figured bv Agassiz in the :<Challenger --Echinoidea is really the .same species as the 

 P. phial,- of Wyv. Thomson. The e.xpression test very nnich prolonged, almost tubular does not 

 seem so ver\' appropriate for the form figured in the Challenger >-Report, and the figure gi\en bv 

 Wyv. Thomson does not resemble the figures of the Cliallengeri-specimen ver\ much either. It 

 seems, indeed, more like the Poiirtalrsia paradoxa described below; but \\'\ v. Tliom son's figure and 

 description of the P. phialc are not sufficiently detailed for deciding the question, and since the type 

 specimen does not seem to exist an\- longer, as I am informed b\- Profes.sor Bell, we must remain at 

 the decision made by Professor Agassiz and let the species described and figured as P.phiale in the 

 Challenger -Echinoidea keep that name. 



Some additions and corrections may be given to Professor Agassi/.' description and figures 

 of the test of this species. Judging from the PI. XXII. a. P'ig. 2 the odd interanibnlatrum is constructed 

 on a rather different plan from what is the case in the other species of Pourtalesite thus far known, 

 representing indeed, the most primiti\e structure of the plastron known among the Pourtalesise; 

 the labrum and sternmn are represented as l)eing in contact with each other, and likewise the ambu- 

 lacra I and V are continuous, the interambnlacra i and 4 not separating the first and the second 

 plates of these two ambulacra. This more primitive structure is the more surprising as this species 

 is otherwise a ver\- modified form. On a careful examination of the specimens in hand, I find, how- 

 ever, that the structure of the test is not as represented by Agassiz; it agrees in the main features 

 with that of the other species. (PL VI. P'igs. i — 2, 7). The labrum is large and carries several primary 

 tubercles; the single plate seen on PL XXII. a. Fig. 2 of the . Challenger -Echinoidea in contact with 

 the aboral end of the labrum and which de Meijere | vSiboga»-Echinoidea. p. 168. PI. XXI. Fig. 417) 

 interprets as the sternum, as it would undoubtedh' have to be interpreted in case the figure were 

 correct, does not reallv exist. In continuation of the labrum follows a pair of large jilates the ambu- 

 lacrals I. a. 2 and V. b. 2, wliich at their aboral end separate a little to give room for a large, single 

 plate, the sternirm, which is again followed by a pair of elongated plates, the episternal plates. The 

 two large plates following the labrum show tlie curious feature of being divided at their oral end b\- 

 a longitudinal line, which does not reach to the middle of the plate. It does not join any other line 

 and thus does not cut off an)- separate plate. This feature I have found quite distinct in the three 

 larger specimens examined by me (among which is one from the Antarctic Sea', from the Oerman 

 Scnith Polar Expedition); in the two smallest specimens I have been unable to trace the limits of the 

 plates with certainty. 



Both the inner plates of the ambulacra I and V are distinct and rather large and in confor- 

 mity with the rule: I. a, II. a, Ill.b etc.; tho.se of the ambulacra II and IV are much .smaller and seem 

 not to be always in accordance with the rule; thus in the specimen figured PL VI. F'ig. 7 the plate 

 II. b was the larger — but the limits of the anterior (especially II. b and I\'. a) of these small 

 plates are generall\- very difficult to see. The pores and tubefeet are distinct ni all the <S inner plates, 

 but there is onh- one in I. a. i and \'. b. i. The plates I. a. 1. b. 1 and \'. a. i. b. i are in contact with 



I In this specimen there is also at the outer end of these plates an indication of such a line: but it does not reach 

 the line from the oral end, so that the plate is not divided. 



