CENTROSTEPHANUS ASTERISCUS. 119 



The calcareous particles in the pedicels are distinctly triradiate, and show 

 little or no tendency to become perforated plates. 

 The sphajridia are not peculiar. 

 This species was not collected by the " Albatross." 



Centrostephanus asteriscus A. Ag. and CI. 



Centrostephanus asteriscus A. Agassiz and Clark. Bull. M. C. Z., L, p. 237. 

 Plates 51, figs. 3-11 ; 55, figs. 1-6; 58, figs. 1-6. 



This very pretty small species is easily distinguished from other members 

 of the genus by the large number of coronal plates and the peculiar abactinal 

 system. In a specimen of 3.5 mm. in diameter there are already eight inter- 

 ambulacral coronal plates and an individual 14 mm. in diameter has thirteen 

 (Pis. 55, figs. 1-3 ; 58, fig. 6), with fifteen or sixteen ambulacral plates, while 

 in a young specimen of C. Eodffersii A. Ag. of 14 mm. there are only nine inter- 

 ambulacral coronal plates, and the large primary tubercles are all placed on the 

 abactinal surface above the ambitus. In asteriscus many are at the ambitus 

 and below it. In a specimen of C coronatus Verrill of 14 mm. there are only 

 eight and nine interambulacral plates, and in the abactinal system the geni- 

 tals are well separated by the oculars which reach the anal system. The 

 latter is covered by fewer and larger plates, more like that of Rodger sii. 

 In Itodgersii the oculars separate the genitals, but scarcely reach the anul 

 system, which is covered by comparatively few large plates, in great contrast 

 to the very numerous plates covering the anal system of asteriscus (Pis. 55, 

 fig. 2 ; 58, fig. Jt). In small specimens of asteriscus the small oculars appear 

 to reach the anal system by the extension of a slightly raised white ridge 

 (PI. 58, fig. 2) running from the median part of each ocular plate and ex- 

 tending to the centre of the anal system, thus forming a conspicuous star 

 on the red abactinal surface. With increasing size the ocular plates are 

 crowded further out by the genitals, which form an independent ring. The 

 genital plates are very uniform in size and shape (heptagonal) and carry three 

 to six distinct miliaries. The madreporic openings are small, forming a narrow 

 band across the promixal part of the right anterior genital (PI. 55; fig 2). The 

 genital openings are well marked and placed near the outer edge of the plates. 



In all the Pacific species of Centrostephanus the radioles are banded 

 with reddish brown upon a lighter shaft ; the bands are fewest, darkest, and 

 widest, and are least distinct in Rodgcrsii, in adult specimens of which they 



