Nematura Bens., a new Genus of Univalves. 217 



of its extending far outside the northern or southern tropics, 

 while the smallest species of Cypras x a range as high as 50° 

 north and south, the larger species being confined to a range' 

 not much exceeding 30° of latitude. 



Art. XI. On Nematura of Benson, a new Genus of Univalve 

 Shells. By G. B. Sowerby, Esq. 



Nem atu n ra is a new genus of univalve marine shells. It 

 was first discovered and described by Benson in the Calcutta 

 Journal of Science. In 1835, he sent me specimens, collected 

 by himself at the mouths of the Ganges. I have never seen 

 his description, nor, of course, have I seen the animal : judg- 

 ing, however, from the nature of the operculum, I suppose it 

 to have been pulmonobranchous. The species he sent to me 

 was named by Benson, in his letters, Nematura DelUe. I have 

 since met with another recent species among some minute 

 shells from the West Indies, and a fossil species from the 

 calcaire grossier, from Grignon and Orglandes. These two 



22 



last species have been in my possession, although unobserved, 

 for several years. I have given specimens of all three to 

 Mr. Gray. The characters of the genus, as far as they can 

 be collected from the shells alone, are as follows : — 



Shell nearly oval, somewhat depressed, rather acuminated 

 posteriorly ; spiral ; volutions few, the last very large and 

 ventricose ; aperture nearly round, placed obliquely and an- 

 teriorly, contracted, and very small in proportion to the last 

 volution ; peritreme continuous ; operculum spiral, horny, 

 of few volutions, somewhat concave externally, rather larger 

 than the aperture. 



At present I am only acquainted with a single shell to 

 which the Nematvirae appear to bear any affinity ; this is the 



Vol. I. — No. 4. n. s. r 



