16 



B. H. GRAVE. 



It appears that most of the individuals of the Pinnidae lack 

 the otocyst altogether. There is not a trace of such an organ to 

 be found in nine tenths of the specimens! In all, I have found 

 only six with otocysts and in these they are highly variable in size 

 and shape. 



Of five specimens of Pinna nobilis from the Mediterranean, not 

 one had an otocyst, and an equal number of specimens of the 



3 4 



FIG. 3. Reconstruction of a particularly compound otocyst. 

 FIG. 4. Drawing of a section of a single capsule of an otocyst, outlined with a 



camera lucida. o, otolith; e, ciliated epithelium; t, ectodermal tube which gave 



rise to the otocyst. 



small red Pinna from Jamaica 1 were examined with the same 

 negative result. 



On anatomical grounds, therefore, one is almost justified in 

 concluding that the otocyst of the Pinnidae is functionless. 



1 I am indebted to Professor E. A. Andrews for specimens of this Jamaican 

 species. 



