98 CRETACEOUS PELECYPODA 



right and only one in the left valve, they could form the basis of a generic distinc- 

 tion. Dunker (Proc. Zool. Soc, 1861, p. 425,) describes several new species of 



14. CleidopJiorm, Hall, 1850, (Pal. New York, ii, p. 300), has been proposed 

 for a palaeozoic form, which in external character resembles Solectirtus and Azov, 

 but nothing is known of the hinge. 



15. Tagelm, Gray, 1847, fSiliquaria, Schuhmacher, 1817, non Siliquarius, 

 alias Siliqtmria, Montf., 1810). Shell, like Solecurtus, elongated, with the beaks 

 nearly central, directed backwards, pallial sinus very deep, reaching anteriorly usually 

 beyond the beaks ; two teeth in the right and two in the left valve, the posterior one 

 in the latter often obsolete, fulcrum supporting a long and strong ligament; 

 surface covered with a concentrically striated, often rough olivaceous epidermis. 



These shells chiefly inhabit the mouths of rivers of the new world ; they have 

 the general character of brackish shells. The animals, so far as they have been 

 examined, have long cylindrical siphons united at the base. 



16. Novaculina, Benson, 1830. Shell transversally elongated, covered with a 

 striated, more or less rough epidermis, beaks sub-anterior, regularly incurved, hinge in 

 the left valve with three diverging teeth, the middle of which is the smallest ; in the 

 right with two teeth, the anterior usually obsoletely bifid, the posterior very oblique ; 

 pallial sinus deep, but not extending anteriorly beyond the region of the beaks; 

 ligament strong, fulcrum not prominent and rather short. The Novaculince inhabit 

 tidal rivers of the eastern hemisphere ; they are the representants of the American 

 Tagelus, but appear to be quite distinct. The siphons of the animal are very long, 

 cylindrical, and separated from the base, the foot is, however, club-shaped. 



Rafinesque appears to have applied to a worn specimen of a Novaoulina the 

 generic name Loncosilla. He states that the hinge has "no teeth as in Anodonta, 

 but a hinge with a marginal nerve, or fold anteriorly, distinct from the margin 

 and a little oblique behind," (see complete writings of C. S. Eafinesque on rec. 

 and foss. Conchology, by Binney and Tryon, 1864, p. 84). The hinge -teeth of 

 Novaoulina, like those of Fharella, are very easily broken away, and there is often 

 no trace of them perceptible in apparently perfectly well preserved specimens. 

 Novaculina has a distinct margin at the hinge and a slight groove extending ante- 

 riorly; it appears therefore very probable ihn.i'RdifLiiQ^quQ'^ Loncosilla solenoides 

 was an old worn specimen of Novaculina gangetica. 



Two such genera, as Novaculina and Tagelus, form, not only in the arrange- 

 ment of the diverging hinge-teeth, but also through the deep pallial sinus, the long 

 and divided siphons of the animals, and their mode of living, a distinct passage to 

 Sanguinolaria, Soletellina, and other typical genera of the next family. 



I Species of Solenidje from cretaceous rocks. 



Eeg-arding the correct generic determination of most of the cretaceous species, only a few 

 suggestions can be made. (See Pictet and Campiche, Pal. Suisse, 4^^ ge^.^ 1864, p. 29, etc.). 



l.—Solen Bupinianus, d'Orb., known only by a fragment perfectly insufficient for deter- 

 mination. 



