24 ASPIDODIADEMA. 



The deep pits at the base of the median ambulacra! area are larger and 

 more numerous than in the Indian species. (PI. VIII. Figs. 2, 3, 5.) The 

 most striking features due to changes of growth are the comparatively late 

 period at which the genital pores are developed, even specimens measuring 

 11 mm. in diameter ( PL VIII. Figs. 7, 8) showing no trace of such openings. 

 The genital plates of earlier stages are markedly pentagonal (PL 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 

 primary tubercles extend also but little above the ambitus. (PL 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. 



Tin' tendency to breaking up of the anal plates already noticed in some of 

 the species of Arbaciadae is shown in some of the younger stages by the ill- 

 defined subdivision lines, such as are represented in Plate VIII. Figs. L5, IS. 



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 

 Temnopleuridae. 



Diadema setosum ('.ray. 



Littoral to 115 fathoms. Florida and West India Islands. 



ASPIDODIADEMA A. Ac. 



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 

 Cidaridae 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. f,i ,. 



I did not notice while examining the Challenger species of the genus 



« Proc. Am. Acad., XIV. 199, L879. 



