OF CONCHOLOGY. 63 



This dentition is in some degree intermediate in character 

 between the Odontoglossata of Gray and the Toxoglossata ; 

 and indicates a new group of value equivalent to these, which 

 may be called Tomoglossata. Probably all of the Clavatu- 

 lime, or PleurotomidiB with an operculum having the nucleus 

 on the inner edge, will be found to belo'ng to it, 



The relations of the genus Halla, the anatomy and dentition 

 of which are described by Fischer in the " Journal de Conchy- 

 liologie,"' vol. Yii., 1858, p. 1-il, will probably be found to lie 

 with this group, rather than with the Defranciini^. That ani- 

 mal has a true lingual ribbon, with the lateral teeth similar in 

 ])osition to those of Cl/oneUa, though much more slender. No 

 rhachidian teeth have been observed. 



Fam. DENTALIIDaE. 



HELONYX, nov. gen. 



Type, H. clavatus. — pi. 9, f. 14. 



Dentalium clavatum Gould, Otia, p. 119. 



Shell small, subulate, polished, almost hyaline, arcuated, 

 swollen before the middle, and contracted at the mouth ; poste- 

 riorly attenuated, with the margin of the anal aperture entire. 

 Foot greatly elongated, cylindrical, and obtuse at the extremity; 

 collar apparently entire. Anal siphon longer than in Dental- 

 ium. not fissured. 



This genus comprises certain small Dtnialvt, which, from 

 the contraction at the anterior extremity of their shells, have 

 been commonly supposed to belong to Annelides allied to 

 Ditrupa. An examination of the living animal in the typical 

 and only living species, D. clavatum.^ discovered by the writer 

 in the harbor of Hong Kong, China, has shown it to be a 

 Mollusk, very closely allied to Dentalium. This species lives 

 on muddy bottoms, at depths of from six to twenty fathoms. 

 It was of a pure waxen-white color when alive, except where 

 the dark-brown rami of the liver showed through the shell. 



The genus, which first appears in the Cretaceous, is repre- 

 sented by several species in the various formations deposited 

 during the Tertiary epoch, when it seems to have reached its 

 climax of development. 



The following are some of the fossil species, for information 

 rewarding^ whicli I am chieflv indebted to Mr. Meek. 



H. PQSILLUS. Deatalium [Ditrupa f) pusillurn Gabb., Palae- 

 ontology of California, I., 1864, p. 139 ; pi. xxi., f. 99. — Creta- 

 ceous formation of California. 



H. SUBCOARCTATUS. Ditrupa suhcoarctata Gabb., Jour. 

 Acad. Nat. Sciences, Philadelphia, [2] iv., 1860, p. 386 ; pi. 

 ixvii., f. 47. — Eocene of Wheelock, Texas. 



