18 ANWALS NEW YORK ACADEMY OF SCIENCES 



The description of this species given hy Brngni^re 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 : Length, 43 mm. ; greatest diameter, 3 mm. ; apical angle, 

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

 Color: White, sparingly dotted with pale brown. 



The protoconch of Oerithium 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 primarv spirals. 

 The lower of the primary spirals becomes graduallv 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 bv 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 extremelv prominent one, all of which are irrejrularlv nodose. 



The median spiral of the bodv volution is spinose on the dorsal side. 

 but on the ventral side the spines are represented bv low nodes onlv. 

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

 coarse spirals with fiuer interoalated ones, and the whole is covered, like 

 the rest of the surface, with the fine costn? described above. 



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

 what flaring-, and crenulated bv the spirals of the outer surface. The 

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

 the outer lin, forms n short cnnnl at the posterior end of the aperture. 

 The anterior canal is short and sliffhtlv curved, and its onening is nar- 

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



