120 



there are no posterolateral rods. The postoral, posterodorsal and posterior 

 rods are fenestrated, excepting for a short distance in the basal part 

 (Fig. 51). The ventral transverse rods are straight and rather broad, not 

 crossing one another with their points. 



Brissus obesus Verrill. 



This species was found in considerable numbers in the sand in shallow 

 water, so shallow as to be quite dry at ebb tide, at the island of Tabo- 

 guilla in the Gulf of 

 Panama ; they were 

 generally lying buried 

 about a decimeter down 

 in the sand. A few ripe 

 specimens were found, 

 fertilization being under- 

 taken on the 7th Janu- 

 ary 1916. The culture 

 was not very good and 

 the larvae did not devel- 

 op so far as to form the 

 posterior process. It was 

 repeatedly tried to start 

 new cultures, but the 

 breeding season had ap- 

 parently ceased already 

 by the end of January, 

 and I did not succeed 

 any more in finding fully 

 ripe specimens which 

 could be used for fertili- 

 zation. Only little information can therefore be given 

 about the larva of this species, the more so as the 

 skeleton of the preserved larvae has been dissolved. Al- 

 though no posterior process had developed before the 

 larvae died, it is beyond doubt that it is present in this larva, since the 

 body skeleton is otherwise of the typical Spatangoid structure. The post- 

 oral rods are fenestrated only in their outer part; the ventral transverse 

 rods are broad as in the Br. Agassizi-larva. Concerning the colour I have 

 only noticed that there is a dark-red pigment spot in the posterior end 

 of the body. 



Fig. 52. Skeleton of the larva of 

 Mcoma grandis. A. ventral view; 

 B. side view. In A. the posterior 

 process has not yet been formed. 

 '""/L Letters as in fig. 51. 



