332 



BALANID^E. 



the growth of the individual. The terminal segments in the longer 

 rami of both the first and third cirrus are antenniformed, — being 

 elongated, and of a different shape, with fewer bristles, compared with 

 the basal segments of the same cirri. It is apparently these terminal 

 segments which are particularly liable to vary in number. In both rami 

 of the third cirrus, some of the segments, from the sixth to the eleventh 

 inclusive, (counting from the bottom), more especially the eighth, ninth, 

 and tenth, carry a few spines coarsely and doubly pectinated ; but as 

 some of the adjoining segments carry spines which may be called 

 doubly serrated, it is not easy to draw an exact line of demarcation. 

 Sometimes, though rarely, a few of the nearly terminal segments in the 

 second cirrus are furnished with similar, doubly pectinated spines. 



Numbers of the segments in the rami of the Cirri, in different 



specimens. 



Varieties. — Under the generic description, I have stated that after 

 having spent some time in examining a very large suite of specimens of 

 T.porosa, I concluded that at least four of the varieties were true species. 

 It so happened that all the specimens which I first examined of the var. 

 (4) rubescens, had the narrow sloping terga, and scuta with only two 

 or three great teeth on their occludent margins ; but ultimately, in a 

 group thus characterised, I found one or two individuals with terga 

 precisely of the shape of those in var. (1) communis. Again, in a group 

 of dull purple specimens of var. commwiis, a few had the narrow 

 sloping terga, and scuta with teeth on their occludent margins, inter- 

 mediate in size and number between the varieties with only one or two 



