ODOSTOMIA. 125 



nucleus concealed : whorls 6-7, rather compressed, rapidly en- 

 larging ; the last occupies nearly two-thirds of the shell : suture 

 more or less oblique, not deep, but-distinct ; the marginal band 

 is observable in young specimens only : mouth more oblong than 

 oval, contracted above, considerably expanded and angulated 

 below ; its length is about three-sevenths of the whole spire : 

 outer lip gently curved, not very prominent : inner lip very 

 slight on the upper part, forming a mere film on the pillar, 

 thickened and decidedly reflected on the lower part, where it 

 is nearly straight : umbilicus none ; the chink, when it exists, 

 is extremely narrow or small : tooth strong, partly concealed ; 

 it is (as usual) placed on the pillar in the middle of the inner 

 lip, just where the reflexion of the latter commences : oper- 

 culum as in the last two species ; the ridge is well marked, 

 and the striation very distinct. L. 0-2. B. 0*1. s. U t>mn. 



Var. 1. crassa. Smaller and thicker; some of the spiral 

 striaB confluent and forming elevated ridges. 0. crassa, Thomp- 

 son, in Ann. & Mag. N. H. xv. p. 315, pi. xix. f. 5. / rd ^ N ^ 



Var. 2. notata. Whorls more convex ; spiral strise more con- 

 spicuous. 0. notata, Jeffr. op. cit. 2nd ser. ii. p. 336. 



Var. 3. angusta. Thinner and more slender. Jeffr. op. cit. 

 3rd ser. iii. pi. iii. f. 18, a, b. 



Monstr. Cylindrical, with flattened whorls ; or having the 

 spire turreted. 



HABITAT : Chiefly (if not only) on the ears of Pecten 

 opercularis and P. maximus, in the coralline zone ; it is 

 widely distributed and rather common. The trawl- 

 refuse at Plymouth and Brixham is especially produc- 

 tive of this shell. Var. 1. Birterbuy Bay, Connemara 

 (M'Calla, fide Thompson, and Barlee); Torquay (Han- 

 ley) . Var. 2. Five miles east of Lerwick, in 40 f. 

 (J. G. J.); a single specimen. Var. 3. Several places 

 from Guernsey to Shetland, but rare ; a specimen of 

 this last variety is nearly a quarter of an inch long, and 

 not a line in breadth. The monstrosities were dredged 

 by Mr. Barlee in Birterbuy Bay. Fossil at Belfast, in 

 a newer pliocene deposit (Grainger) ; Clyde beds (Cross- 



