18 ANNALS NEW YORK ACAD'EMY OF SCIENCES 



The description of this species given by Bruguiere is closely similar to 

 that of Adanson, and much of it is even worded in the same way. Prac- 

 tically the only addition made by Bruguiere was in giving the species a 

 binomial name. 



Measurements : Leng:th, 43 mm. ; greatest diameter, 3 mm. ; apical angle, 

 50° to the eiiibth volution, changing to 31.5° ; sutural angle, 72.5°. 

 Color : White, sparingly dotted with pale brown. 



The protoconch of Cerithium adansoni consists of about one and one- 

 fourth volutions. The ornamentation begins as two spirals crossed by 

 distant ribs on the first volution beyond the protoconch (plate iii, fig. 2), 

 The second volution bears three fine spirals on the shoulder. These 

 are increased by a fourth fine spiral on the third volution, and an 

 intercalated spiral appears between the two primary ones. Tertiary 

 spirals and those of higher order are soon developed, and these fine spirals 

 do not increase greatly in size, but they become extremely numerous, so 

 that the entire surface of the adult is covered with thread-like costge. On 

 the fourth volution, just below the upper suture, there is an elevation of 

 the surface to form a coarse spiral which carries with it the fine spirals 

 already existing. Later in the life of the shell other coarse spirals arise 

 in a similar manner on the shoulder and below the two primary spirals. 

 The lower of the primary spirals becomes gradually weaker and the upper 

 more prominent, until at about the sixth volution the outline of the 

 whorl has lost its vertical element formed by the two equal spirals and 

 has become an acute angle. On the next volution the center of the rib 

 becomes so prominent that it might almost be called a spine, and on this 

 volution also rows of large nodes are formed by the breaking up of the 

 coarse spirals just below the upper suture and above the lower one. On 

 the eleventh volution there are three coarse spirals above and three below 

 the central extremely prominent one, all of which are irregularly nodose. 



The median spiral of the body volution is spinose on the dorsal side, 

 but on the ventral side the spines are represented by low nodes only. 

 Below the prominent spiral on the body volution there are six or more 

 coarse spirals with finer intercalated ones, and the whole is covered, like 

 the rest of the surface, with the fine costre described above. 



The aperture is a broad oval in outline. The outer lip is thick, some- 

 what flaring, and crenulated by the spirals of the obiter surface. The 

 inner lip has a thick callus, raised into a strong blunt tooth which, with 

 the outer lip. forms a short canal at the posterior end of the aperture. 

 The anterior canal is short and slightly curved, and its opening is nar- 

 rowed by the rapid growth of the lower portion of the outer lip. This 



