OF SOUTHERN INDIA. 309 



The genera which I shall refer to the present family are : CurtonoUis^ SchizO' 

 dus, Neoschizodus, MyopJioria, Trigonia, Meekia and Remondia, The first is based 

 upon a Devonian and the second upon a Permian species, the third and fourth are 

 triassic, the fifth is chiefly Jurassic and cretaceous ; in tertiary rocks already Trigonioe 

 are very rare, and only one type (the TectinatcB) extends into the present (Austra- 

 lian) seas ; the two last named genera are proposed for peculiar cretaceous shells, 

 which may already occur in the jurassics. This shows the geological development 

 of the family. The older forms, like ScMzodiis and Myophoria^ principally differ 

 from Trigonia by the want of the grooves or strige on the hinge-teeth, while Remon- 

 dia and Meehia seem to indicate, by the larger number and distribution of the sul- 

 cated hinge-ribs, a strong relation to the Crassatellid^. Further details will be 

 found in the characteristics given of the different genera. With reference to the 

 genus Verticordia (and the several forms identical with it), classed in the present 

 family by H. and A Adams, I have already observed, that its proper place appears 

 to be in the GJEEAMACEA fvide p. 224). It is difficult to explain the peculiar 

 assemblage of fossil genera, referred to this family by Chenu in his Man. de Conch. 

 I should almost think it must be an accidental error, though Mr. Chenu' s classi- 

 fication of fossil genera is by no means free from blunders. 



1. Ciirtonotus, Salter, 1863, ( P1855), (Quart. Journ. Geol. Soc, Lond., xix, 

 p. 494). Shell elongately ovate, moderately tumid, sub-equilateral or inequilateral, 

 with the beaks almost anterior ; hinge in the right valve with two diverging sub- 

 marginal cardinal teeth separated by a large pit, the anterior tooth being stronger 

 than the posterior ; left valve with a large median and, on each side, one sub-obsolete 

 marginal cardinal ; muscular scars very elongated, pallial impression distant from 

 the margin of the shell, which is smooth; type, (7. elongatus^ Salt. (1. cit., p. 495, 

 fig. 5). Salter refers a few Devonian species to this genus. It seems very closely 

 allied to King's ScMzodus, but has not the broad median emarginated tooth in the 

 left valve fitting into a special pit of the right valve ; the forms of Curtonotm are 

 also much more regularly oval. 



2. ScUzodus, King, 1844, (Perm. foss. of England, &c., 1850, p. 185). Shell 

 obliquely ovate, posteriorly somewhat produced, moderately tumid in front, with the 

 beaks close together, incurved and sub-terminal ; hinge of right valve with two 

 diverging sub-marginal cardinal teeth, of left valve with three cardinal teeth, one 

 marginal on each side and a median largest, more or less distinctly bifid ; surface 

 smooth, or with fine concentric, and sometimes also with a few radiating, lines ; type, 

 Sch. ohsGuriis, Sow. This species was described by Sowerby SLsAximis, but the first 

 species noted by the author under this last genus is a quite distinct tellinoid shell 

 from the London clay, Axinus angulatus^ and consequently the present genus cannot 

 be identified with Axinus, as has been done by various writers. Species of Schizodus 

 have been mostly described from the upper palaeozoic rocks ; lately there have also 

 some triassic species been referred to it, (Ann. des sc. geologiques, Hebert and 

 M. Edwards, I, 1869, p. 136), but it does not seem certain whether they belong to 

 this or to the next genus ; in fact the generic determination of these shells appears 

 to me to be quite problematic. 



