108 THE VOYAGE OF H.M.S. CHALLENGER. 



Temnopleurus toreumaticus. 



Cidaris toreumaticu, Klein., 1734, Nat. Disp. Ech. 

 Temnopleurus toreumatieus, Agassiz, 1841, Int. Mon. Scut. 



Station 203. October 31, 1874. Lat. 11° 7' N., long. 123° 7' E.; 12 to 20 fathoms; 

 mud. 



Pleurechinus (Temnopleurus). 



Pleurechinus, A. Agassiz, 1841, Int. Mon. Scut, 



Pleurechinus hothyroides (PI. X." figs. 1,2). ' 



Pleurechinus hothryoides, Agassiz, 1841, Int. Mon. Scut. 



The Challenger collected three small specimens of a Temnopleurid, which I am 

 inclined to refer to the sub-genus Pleurechinus, Agassiz (see Revis. Echini, p. 465); 

 they are unfortunately not large enough to compare .directly with the typical Pleurechinus 

 hothryoides. They show clearly, however, that we may expect to find in the China Seas a 

 species of Temnopleurus still retaining the principal features so characteristic of some of 

 the nummulitic species of India, figured by D'Archiac and Haime (Animaux fossiles de 

 rinde, see Plate XIII. fig. 7, of Temnopleurus valenciennesi) , to which the specimens of 

 the Challenger are most closely allied. The outline of the test, even in these young sjDeci- 

 mens, measuring (the largest) not more than 18 mm. in diameter, is high, resembling 

 already -somewhat the globular shape of such species of Amhhjpncustes as Amhlypneustes 

 griseus, and difiering from the other species of Temnopleurid^ in which the outline of 

 the test is quite conical at a corresponding stage. The genital ring (PL X.'' fig. 1) is 

 narrow, compact, slightly pentagonal; the genital plates are of uniform size, with the ex- 

 ception of the madreporic genital which is somewhat larger and rectangular in outline, 

 the pores covering its entire surface with the exception of the space occupied by the ring 

 of secondary tubercles, which runs along the inner edge of the genital plates, separating 

 them from the anal system (PL X." fig. 1). In addition to this edging of secondar}' 

 tubercles, the genital plates' carry from two to three similar tubercles irregularly placed 

 on the plates and a few miliaries. The genital openings are deep crescent-shaped notches, 

 cut out of the outer edge of the plates; the genital plates are united along the anal edge, 

 and a distinct pit in the angle of the sutures between the genital and ocular plates 

 separates the latter from the edge of the anal system. The anal system is covered by 

 an outer row of large triangular plates with smaller slender elongate plates arranged 

 round the anal openings. In the interambulacral area there are two disconnected 

 elliptical pits at the two extremities of the horizontal sutures, separating the coronal 

 plates (PL X.* fig. 2). The coronal plates carry from one to three large primary 

 tubercles arranged in a horizontal row near the lower edge of the plate, with a 

 somewhat undulating horizontal line of smaller secondary tubercles above that, the 



