114 CRETACEOUS PELECYPODA 



peculiarities in common, and were on that account placed in distinct sub-o-enera ; 

 these sub-divisions appear to me rather desirable. 



la. Fsammohella, Gray, 1851, (??=AmpMGhcena, Philippi). Shells similar to 

 those of Gari, but smoother, the posterior part slightly ridged, and the termination 

 more rounded ; hinge usually with two blunt, partially grooved teeth in each valve. 

 G. modesta oi Deshayes maybe considered as the type of this sub-genus; the 

 forms are intermediate between those of true Gari and of the next sub-genus. It 

 seems very doubtful that Philippi's name AmpUclicBna can be applied to this sub- 

 division, when we compare the characteristic given by that author in his Manual 

 of Conchology. I shall notice the genus further on as distinct. 



16. Fsammocola, Blainv., 1824. Shell rather solid, with sub-parallel upper 

 and lower margins, posterior part generally somewhat longer, obliquely truncated. 

 The type of this sub-genus is Fsammobia maxima^ Desh., it is a form which mostly 

 approaches some of the prautillinm. 



2. '' AmpMchcena,'' Phil., 184^7, (Handb. der Conch., 1853, p. 307). ^' Shell 

 elongated, nearly lineal and equilateral, gaping at both ends ; beaks small ; car- 

 dinal teeth f, no laterals; ligament external, placed on slightly prominent fulcra; 

 two muscular impressions ; pallial sinus large. This genus apparently stands between 

 JDonctx and Solen ;'^ one species. A, Sindermanni^ is from Mazatlan. Such is the 

 characteristic given by Philippi; I do not know the species, but it appears 

 rather distinct from other Fsammohellce, 



There have been a large number of fossil species described under the generic 

 name of Gari or Fsammobia, but it remains to be shown how many of them really 

 belong to that genus, or even to this sub-family. It cannot be doubted that true 

 species of gaeinjs occur in tertiary deposits, but those from cretaceous and older 

 deposits seem to a large extent doubtful. I have ascertained that some of the cre- 

 taceous species which in external form perfectly resemble Gari (sub-genus Fsammo- 

 cola) do not at all belong to that genus, but to Tapes^ or one of its nearly allied 

 genera. In the list of the cretaceous species I shall, however, be obliged to retain 

 some under the name Gari^ for unless the hinges of those species have been exa- 

 mined, there is no advantage in shifting them to other genera. 



3. Miatula, Modeer, 1793, (Soletellina^ Blainv., 1824). Shell elouo'ated 

 gaping at both ends, thin, covered with a thick horny epidermis, posteriorly 

 less high and more or less produced, flexuous and slightly carinated; hino'e usually 

 with two cardinal teeth in each valve, but the posterior in the left valve is generally 



smaller, laminar, and becomes occasionally obsolete ; pallial sinus large. The type 



of this genus, as restricted, is Linne's Solen Biphos. The species, as a rule, 

 greatly resemble those of Gari, and could be considered only as sub-generically 

 distinct from them, but while the latter are truly marine shells, the EiatulcB 

 generally live near rivers and in brackish water, having a thinner shell, but with 

 more strongly developed epidermis; the posterior end of the shell is also more 

 attenuated and flexuous than in Gari, 



