ANATOMY AND LIFE HISTORY OF MOLLUSCA. 157 



there are rounded and irregularly-shaped nacreous nodules, like 

 the pores which one sees on the inside of the freshwater mussel. 



We will now turn to the consideration of the structure of a 

 non-nacreous shell, namely Cerithium ebeninum, Bruguiere : a 

 turriculated univalve shell, common at Port Jackson. (See fig. 5 

 back and front views of shell.) It has ten or eleven whorls 

 usually ; is conspicuously nodose, and spirally grooved ; of 

 uniform dull brown colour, a spreading mouth and highly 

 enamelled interior. Around the mouth there is a margin of rich 

 brown colour on the outer lip and then an irregular brownish- 

 white interval, streaked and clouded with a deeper fawn-colour, 

 until in the throat it merges into a uniform deep chocolate-brown. 

 If a section be made of the shell the brilliancy and glassy 

 smooth polish of the enamel in the upper chambers of the spire 

 render it a most beautiful and interesting object. It is often a 

 wonder to me that shells are not more largely used for decorative 

 and ornamental purposes than they are. This species cut in half 

 shows such brilliancy and beauty of colour inside that with a little 

 manipulation it could be manufactured into an attractive brooch. 



The highly enamelled lining is banded or clouded by a rich 

 reddish-brown, which on the opaque outside deepens almost 

 into a black colour. Under the microscope the enamel is seen to be 

 colored by very fine lines of reddish-brown membranewhich permeate 

 the whole shelly substance. Sections of the shell show transverse 

 waving-Iines of a rich reddish-brown intercalated with strata of 

 lighter colour, or even white in extremely fine lines proceeding from 

 the columella to the shell-surface. These lines though waved and 

 curved, are crossed irregularly by transparent lines of what I 

 consider to be nerve-fibres which divaricate and anastomose until 

 they terminate on the floor of the whorl or outside of the shell. 



It is difficult to make this understood without a great number 

 of sections, for the structure is so extremely complicated ; but I 

 believe its explanation to be as follows : — there is a nerve-ganglion 

 in the columella of the shell, which is found in a spiral line through 

 its centre and for the whole of its extent. It is of a reddish-brown 

 colour and of silky lustre. The nerve-fibres which proceed from 

 it through the shelly matter run in closely parallel lines to the 

 outer or inner lining of the shell. They curve apart in lines of 

 two different directions according as they are intended for the 

 inner or outer surface, out of which they pass by the tubes already 

 referred to. A section of the whole shell shows the inner lining 

 of the whorls to be a thin transparent stratum penetrated by 

 innumerable pores. In this species they are not so visible on the 

 outer surface. 



It will be observed from this description of Patella tramoserica, 

 Martyn, and Cerithium ebeninum, Brug., that there is a distinct 



