238 INVERTEBRATA OF MASSACHUSETTS. 



turity in its callus, the umbilicus, and the color of the throat, suf- 

 ficiently distinguish it from both N. duplicdta and N. heros. 



Natica clausa. 



Shell sub-globose, more or less tinged with brown ; umbilicus 

 closed ; operculum calcareous. 



Figure 167. 



State Coll., No. 45. Society's Coll., No. 952. 



Natica clausa, Brod. and Sowerby ; Zool. Journ., iv. 360. Gray; Zool. of 



Bceclmjs Voy., 136, pi. 37, f. 6, and pi. 34, f. 3. 

 Natica consolidata, Couthouy ; Bost. Journ. Kat. Hist., ii. 89, pi. 3, f. 14. 

 Natica borealis, Beck ; (not Gray) teste Loven. 



Shell small, sub- globular, surface of a dim lustre, marked by 

 striae of growth only ; color from a livid-white, to dark reddish- 

 brown, those of the latter tint exhibiting conspicuously a zone of 

 the former color at the base ; epidermis thin, bony, brownish 

 horn-color ; whorls four or five, tumid, but a portion near the 

 sutures is slightly depressed ; spire slightly elevated, obtuse ; 

 suture well defined ; aperture oval, unusually wide behind ; outer 

 lip sharp, thickened and rounded as it ascends to the umbilicus, 

 which is completely consolidated by an ivory-white, shining 

 callus ; on the whorl the callus is thin, but a free deposit of it 

 within the angle firmly supports the junction of the lip to the 

 whorl, a zone of which calcareous deposit also surrounds the 

 umbilical region ; throat white ; operculum calcareous, bluish- 

 white. Length || inch, breadth |i inch. 



Taken alive from the stomachs of fishes, plentifully. 



This species is readily distinguished from all others of our coast by 

 its bony operculum, and by its small umbilicus, into which just enough 

 of white callus seems to have been crowded to fill it accurately. 



Mr. Sowerby, on actual comparison, declares this to be his N. 

 clausa ; and, as his description was published several years prior to 

 that given by Mr. Couthouy, his name must take precedence. Mr. 

 Sowerby states it to be nearly an inch in diameter ; whereas the dimen- 

 sions above given exceed those of the specimens usually found with 

 us. But, as it is evidently an Arctic shell, Mr. Sowerby's specimens 

 having been brought from Melville's Island, and I have seen one from 

 the Banks quite as large as those he mentions, I insert also the name 

 given to it by Beck, on the authority of Dr. Loven. 



