76 



their development the question cannot, of course, be regarded as settled ; 

 but there is reason to expect that a complete study of their development 

 will show them to be quite distinct. 



Echinometra van Brunti A. Ag. 



Fertihzation of this species was tried repeatedly in the beginning of 

 November 1915 at Taboga, Panama, but always with poor success, it 

 being at the end of its breeding season. Some of the embryos reached the 

 young Pluteus stage. In the few preserved specimens the skeleton has been 

 dissolved. No remarks about its structure being found in my notebook, 

 I can only state from memory that the body skeleton forms a basket 

 structure, but whether the recurrent rod is double or not, unfortunately, 

 must remain uncertain. The body is very obliquely truncated. 



Colobocentrotus atratus (Linn.) 



PL XII, Figs. 4—5. 



This species occurs in great numbers on the rocky coasts of Hawaii, 

 near Hilo, always in places exposed to the most violent surf. Fertilization 

 was undertaken on April 4th; the culture proved successful. About the 

 early development stages 1 have only noticed that gastrulation had taken 

 place at the age of 24 hours and that the young Pluteus stage was reached 

 on the second day. The larvse developed normally for about two weeks, 

 when all died away. New fertilization was then undertaken, but with 

 poor result, it being about the end of its breeding season. Information 

 can thus be given only of the first larval stage, and, moreover, only in- 

 complete, the skeleton having been completely dissolved in all the pre- 

 served specimens. (There was no possibility of making drawings from the 

 living specimens). 



The shape of the larva in the first stage is quite characteristic on account 

 of the unusual width of the posterior end (PI. XII, Fig. 5). A sketch made 

 from a living specimen shows that the skeleton passes close to the stomach, 

 the posterior end of the body being thus much broader than the supporting 

 skeletal structure. The body is otherwise short, obhquely truncate as in the 

 Echinometra larva. The postoral band has a downward sinuation at each 

 side, which indicates the presence of ciliated lobes; on the sides of the body 

 the vibratile band goes down almost to the posterior end, which fact, 

 combined with the unusual width of the posterior end, indicates the pre- 

 sence of posterolateral processes in the fully formed larva. The postoral 

 arms long, diverging, rather broad (probably somewhat broader than 

 shown in the figure). The suboral cavity is very deep, with a little eleva- 



