24 ASPIDODIADEMA. 
The deep pits at the base of the median ambulacral area are large:- and 
more numerous than in tlie Indian species. (Ph VIII. Figs. 2, 3, 5.) The 
most striking features due to changes of growth are the compai'atively late 
period at which the genital pores are developed, even specimens measuring 
11 mm. in diameter (Pi. VIII. Figs. 7, 8) showing no trace of snch openings. 
The genital plates of earlier stages are markedly pentagonal (PI. VIII. Figs. 
11, 12, 15, 18); the granulation of the anal edge of the genital plates is 
a character not found in the younger stages. In these young stages the 
jirimary tubercles extend also but little above the ambitus. (PI. VIII. Figs. 
7, 11, 15.) In Figure 15 the primary interambulacral tubercles are limited to 
the actinal surface, and the primary interambulacral tubercles extend at first 
but little towards the abactinal part of the ambulacral area. Compare Plate 
VIII. Figs. 7, 11, 15, and Plate VIII. Fig. 1, with their corresponding profile 
figures. The resemblance of these young stages of Coelopleurus to some of 
the Cretaceous and Jurassic Echini, such as Tiarechinus, etc., is very striking. 
The tendency to breaking up of the anal plates already noticed in some of 
the species of Ai'baciada3 is shown in some of the younger stages by the ill- 
defined subdivision lines, such as are represented in Plate VIII. Figs. 15, 18. 
The function of the ambulacral pits of this genus I have been unable to 
ascertain. The sutures present no trace whatever, in the specimens I have 
examined, of the remarkable dovetailing observed by Duncan in the pitted 
Temnopleuridte. 
Diadema setosum Gray. 
Littoral to 115 fathoms. Florida and West India Islands. 
ASPIDODIADEMA A. Ag. 
A marked feature of this genus is the nearly uniform size of the secondary 
radioles, both in the ambulacral and interambulacral areas. This charac- 
ter is a structural feature which Aspidodiadema has in common with the 
Cidarida3 in addition to their similar abactinal system, to the structure of 
the ambulacral areas, etc. ; features to which I have already called atten- 
tion in the Preliminary Report of the Challenger Echini,* and in the final 
Report (p. 64). 
I did not notice while examining the Challenger species of the genus 
* Proc. Am. Acad., XIV. 199, 1879. 
