Ill CRETACEOUS PELECYPODA 



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

 these sub-divisions appear to me rather desirable. 



la. Fsammobella, Gray, 1851, (??=AmpMclicena, 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. modestaoi 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 Amphichcena 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. 



1 b. 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 Psammobia 7naxima, Desh., it is a form which mostly 

 approaches some of the prarellinje. 



2. "Amphichcena;' Phil., 1847, (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 

 Donace and Solen ;" one species, ^. Hindermanni, is fvom Mazatlan. Such is the 

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

 rather distinct from other PsammobellcB. 



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

 name of Gari or Psammobia, 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 gauinm 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 Psammo- 

 cola) do not at all belong to that genus, but to Tap)es, 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. Eiatula, Modeer, 1793, CSoletellina, Blainv., 1824). Shell elongated, 

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

 less high and more or less produced, flexuous and slightly cariuated ; hinge 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 genvis, as restricted, is Linne's Solen Diphos. The species, as a rule, 

 greatly resemble those of Ga}'i, and could be considered only as sub-generically 

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

 "■enerally 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 flesu.ovis than in Gari. 



