OP SOUTHERN INDIA. 159 



species belonging to this sub-family known ; somewhat or scarcely half the number 

 of species is known from tertiary deposits, about one-third from the cretaceous, 

 and about one-fourth, or perhaps less, from the jurassics, (unless the species of 

 EripJiyla turn out to be particularly numerous). 



List of ceetaceous species oe Venerid^. 



In enumerating' the cretaceous species belonging to the present family, I shall first note those 

 mentioned by Pictet and Campiche, who refer them summarily to the single genus Venus, which 

 the authors adopt in Linne's sense, (Paleont. Suisse, 4"^^ ger., 3«^e p^rt., p. 186,1865). It is 

 surprising to meet with such a treatment of this interesting group of shells in the hands of a 

 celebrated PalsBontologist like Pictet, who considers Tapes, Cytherea, and Dosinia as in some res- 

 pects inferior sub-divisions of Venus, Surely the hinge-teeth of a good many cretaceous species have 

 been examined, and it seems to me a very wrong principle to ignore those, — even were they only 

 few, — because we do not know the hinges of all the species. Under such circumstances fossil 

 conchology would never have a chance of becoming more than a helpless instrument in the hands of 

 those who wish to make use of it in the identification of strata. No doubt, if this object were 

 only attained, it would possess its great value. However, I fear that even those casts upon which 

 Pictet and Campiche, and many others,^ base their species, and of which they say that they are 

 merely intended for assisting in the study of the relations of different beds in which they occur, 

 are of very little use to the geologist. It is extremely difficult to identify strata by such casts, 

 which no field geologist will deny ; and if specimens are found with the shells preserved, a determin- 

 ation of the species becomes extremely difficult, for the shells of the Veneridm often possess near 

 the margins and especially at the beaks such thickness that it is impossible to make more than a 

 very generally correct conclusion from the form of the one as to that of the other. 



These introductions of very imperfect fossil species are also objectionable for another reason, 

 because they often involve unnecessary changes in specific names, as has, for instance, been largely 

 done by d''Orbigny. Many of the original specific names have to be again restored as soon as a 

 correct generic determination of the shells has been obtained. 



The list of the cretaceous species which I give here must be considered for the present only as a 

 very poor attempt at a revision of the numerous cretaceous forms, but much may be done by 

 those who have a large stock of materials accessible, for since the publication of the first descriptions 

 of many of the fossils better specimens have no doubt been obtained. I was myself fortunate enough 

 to see several during my visit to Europe in 1867. I need only remark that the observation of an 

 anterior impression of a tooth in front of the beaks does not in all cases warrant the conclusion 

 that the shell was one of the Cytlierea group, because I have already explained that in Venus as 

 well as Cytherea the lunular teeth are analogous, and the difference lies in a modification of the 

 true cardinals j this to some extent also applies to the tapesin^, 



1. — Venus suh'Brongniartiana, d''Orb., (Brongniartiana, Leym.,) agrees in general cliaracter 

 partially with Tapes, partially with (7(^^/i5^«, or it may even be an elongated Cyprimeria. Schaf- 

 hseutl (Siid. Bayerns Leth. Geog., 1863, p. 170, pi. xliii, fig. 2,) refers to this a species which is 

 similar in form, but decidedly much thicker ; the figured specimen is a cast and the pallial line is 

 shown entire ; it is likely quite a different shell from the above. 



2. — V, Ricordeana, d''Orb., has the form of a compressed Cytlierea. 



3. — V, Mutronensis, d^Orb., may be a Tapes. 



4-5. — V. Rohmaldina and Cornueliana of d^Orb. recall some forms of Calllsta. 



* The so-called species of shells described by Co qu and in his work on Constantine, and also in the Monograph of 

 the Etage Aptien of Spain, as Hkewise those in Loriol's worii on the fossils of the Monte Saleve, are formed with 

 but Httle regard to the generic characters, and are to a great extent useless. 



