REPORT ON THE ECHINOIDEA. 153 



' summit, wliicli is somewhat raised ; these radiating ridges give to the abactinal part of 

 the test (PL XXIX.*" fig. 3) quite a variegated appearance, as they are somewhat darker 

 in colour than the groundwork of the plate itself. The outline of the test is extremely 

 variable, fully as variable as that of some of the sj)ecies of Galerites and Ananchytes. 

 The actinal interambulacral plate adjoining the actinost'ome is slightly turned up in the 

 interior of the test, and forms a thin ridge similar to the ridge connecting the auricles 

 in genera provided with teeth. The ovaries (PL XXIX.'' fig. -13) are thick close clusters 

 of short grape-like processes ; there are four genital plates, all of which carry genital organs 

 equally developed. The large size of the ampuUge of the ambulacral tentacles is remark- 

 able, they are developed into large vesicles round the actinal region (PL XXIX.*" fig. 6). 



The membrane of the actinostome of the younger specimens is strengthened by a 

 smaller number of larger plates, forming a single row, in the centre of M-hich, on the 

 posterior edge of the actinal opening, are placed seven to eight smaller plates irregularly 

 arranged (PL XXIX." fig. 18). 



This arrangement diS'ers materially from that figured on Plate XXIX.** fig. 5, of a 

 lai'ge specimen, in which the secondary plates of the actinal membrane have become 

 nearly as large as the primary row. In the actinostome of the larger specimens there 

 is the least possible indication of a rudimentary bourrelet in the crowding of the 

 three or four primary tubercles, on the actinal edge of the narrow interambulacral j^late 

 adjoining the actinostome (PL XXIX.* fig. 5). There is no trace of this in the younger 

 specimens (PL XXIX. " figs. 16, 18) ; although the primary tubercles are large, yet they 

 are not closely crowded together as in older specimens. The actinal opening is 

 generally transversely elliptical (PL XXIX.** figs. 2, 5), but this is by no means 

 constant, as it is in some cases nearly circular (PL XXIX.'' fig. 18). The apical 

 system (PL XXIX.'' fig. 14) is disconnected, two* of the genital plates belonging to the 

 trivium, and two to the Ijivium, separated by large intercalated interambulacral 

 plates, upon one of which the madi'cporic body often encroaches, and is in some cases 

 placed entirely upon one of the intercalated interambulacral plates. The anal system is 

 vertically elongated, strengthened by an outer row of large plates (PL XXIX.* fig. 20) 

 with a number of smaller plates immediately round the anal opening. An interior \dew 

 shows that the termination of the alimentary canal is sudden, forming a short intestine 

 (PL XXIX. ''fig. 19). 



In young specimens (PL XXIX." figs. 1-12) the test is flattened, the outline seen in 

 profile is regularly arched, rounded anteriorly and posteriorly, and passing very gradually 

 to a flattened actinal surface. Seen facing the posterior extremity the test is similarly 

 regularly arched (PL XXIX.* fig. 11), the apical system and apex coincident and central, 

 the posterior extremity when seen from above, but slightly smaller than the anterior 

 (PL XXIX.* figs. 1, 5, 9). The anal opening, however, is already placed on the actinal 

 surface in the youngest of the specimens collected. 



(ZOOL. CHALL. EXP. — PAKT IX. — 1881.) I 20 



