286 BULLETIN OF THE 



on<lary tubercles, the principal rows of ambulacra! and interambula- 

 cral tubercles being very prominent. The buccal membrane and abactinal 

 system present no striking differences, the anal plates being only four 

 in number in all the specimens collected. In Genocidaris, of which an 

 extensive series was collected, we find in the smallest specimens a few 

 large spines, resembling the spines of young Dorocidaris abyssicola, 

 equalling in length the diameter of the test. As the specimens increase, 

 the spines lose their spindle-shaped form and their serrate edge ; they 

 become more pointed and elongate, diminishing rapidly in proportion to 

 the size of the test, and soon take the proportions they have in the 

 adult. The actinal opening is very large at first, the test in young 

 specimens being a narrow ring when seen from the actinal side. The 

 primary tubercles are few in number, with remarkably prominent ridges 

 radiating from them, leaving deep pits between the ridges. With in- 

 creasing size these ridges become miliaries and secondary tubercles, the 

 pits, however, remaining round the boss of the primary tubercles in both 

 the areas ; so that the test passes through stages in which it resembles 

 at first young Psammechinus, then a Psammechinus with deep grooves 

 radiating from the tubercles, and finally with deep pits round their base. 

 The subanal plate retains always its preponderance, and the embryonic 

 character of the anal system (retained in the generic name) is a marked 

 feature of this interesting Sea-urchin. The actinal opening rapidly be- 

 comes smaller, and resembles that of Psammechinus. In fact, Geno- 

 cidaris might be called a Psammechinus among Temnopleuridai, while 

 Toreumatica is the Lytechinus of the family. 



The changes taking place in the arrangement of the pores in Trip- 

 neustes and Boletia are similar to those observed in Echinus ; at first a 

 simple vertical row, then arcs laterally curved, then three pairs of pores 

 for each ambulacral plate, in oblique open curves, and finally almost 

 horizontal curves, the pores appearing to be placed in independent 

 vertical rows. Hipponbe of Gray cannot be retained, the name being 

 preoccupied by Audouin, and as Hipponoe and Tripneustes are 

 identical, the name Tripneustes can be retained to include the species of 

 both these genera. 



Among the Clypeastroids we find in the young during their growth 

 greal changes of form and structure taking place. In young Kchin- 

 arachnius the outline is elliptical, the test is arched, high, the anus is 

 placed in a slight depression of the test, and, seen in profile, we are re- 



