OCR Text |
Show 46 MR. F. J. BELL ON A NEW GENUS OF ECHINOIDS. [Feb. 3, specimen the difference between the outer and inner pore can still be observed, just as well as in the upper portion of the rows. What, however, is more remarkable now remains to be noted : the outer row of pores may be traced from the point where they cease to be accompanied by the inner row as far as the actinal region, and that with complete regularity of spacing, and in lines which only here and there diverge from being completely straight; when they reach the phyllode they of course exhibit some modi-cation ; but that is of no importance for the moment. What we have here is the regular repartition of one row of pores from the apical to the oral pole. In this, as in several other points, the specimen under description approaches the genus Conoclypeus, the existence of which in the present epoch has been lately signalized by Prof. Alex. Agassiz1 : in Conoclypeus sigsbei the paired arrangement of the ambulacral pores does not extend over more than two thirds of the abactinal surface, while C. anachoreta, Agassiz (L.), is seen to retain the paired arrangement from the apical to the oral area (see Desor, Echinides fossiles, pl. xxxiii. figs. 5-7). W e may find, then: the following series:- Conoclypeus anachoreta : pores in pairs extend over the whole of the ambulacral area. Palceolampas, nov. gen.: pores in pairs extend to the ambitus; outer row extend to the peristome regularly. Conoclypeus sigsbei: pores in pairs extend over part only of the abactinal area; outer rows as in Palceolampas. Echinolampas: pores of corresponding paired rows unequal. E. depressa: pores of outer rows extend regularly to actinostome. E. oviformis: pores of outer row not regularly distributed on the plates between ambitus and actinostome. Neolampas: pores in single row (paired arrangement altogether lost). Whether the mass of their characters is not such as to justify the union of C. anachoreta and C. sigsbei in a single genus, and the generic separation of the new form (Palceolampas), is a point which I will discuss later on. The table as here arranged, seems to throw discredit on the union of Echinolampas depressa and E. oviformis in the same genus ; but there are other points of importance in the structure of the Echinoderm than the characters of the ambulacral system, and these must have their due weight. The bourrelets of the actinal system are distinct, but they do not project into the buccal cavity ; they are well rounded, not pointed at all, and may be said to be due rather to the development of the phyllodes, which mark off the interambulacral periphery of the actinostome, than to any modification in the interambulacral plates themselves; judging from the photograph of C. sigsbei, they are less developed than in that new form, while they have no such sharp projection as in Echinolampas oviformis ; the outer row of pores bends slightly outwards, and then inwards so as to approach its fellow; 1 Bull. Mus. Comp. Zoology, v. no. 9, p. 190. |