OF SOUTHERN INDIA. 441 



retained Parkiusou's name Harpax (ISll), but I do not think that the distinction 

 is really a generic one; (Essai s. les Plic. foss., &c., Mem. Soc, Linn, de Norm., 

 1859, XI, p. 1 et seq.). The general character and structure of the shell is in both 

 essentially the same, the hinge-teeth in Karpax always extend up to the beak, the 

 ligamental pit is in the right, or attached, valve at the end of a strong median 

 rib, and in the left valve it is very slightly marked, while in FUcatula there is 

 usually a small space between the beak and the hinge, separating the teeth from 

 the beak itself, and the ligamental pit in the left, or free, valve is conspicuously 

 deepened. Besides that the hinge-teelh of Sarpax are generally stronger and more 

 parallel, and the shells are often of large size. It may be thought convenient 

 to retain the name Harpax sub-gene rically for such characteristic forms as 

 a. Terquemi,Y^^xf\..-Ti&%\., but as the left or free valve of some recent PZica^«^<r<? 

 offers characters of the hinge-teeth which are nearly identical with those of Harpax, 

 it would not be justifiable to recognise the latter as a separate genus. 



1^;. In the above quoted paper (p. 113 et seq.), Eudes-Deslongchamps dis- 

 tinguished among the mesozoic Plicatulce a peculiar section under the name 

 Fl. retictilatce. They are sessile with the greater part of one valve, of a semi- 

 circular shape, and the inner surface is always peculiarly striated and reticulated. 

 The hinge areas of both valves are obliquely descending, and there appears to be 

 a median ligamental pit present, but whether for tlie attachment of a ligament or 

 not is uncertain ; no hinge-teeth, nor a pallial line, or muscular scars, have as yet 

 been observed in these fossils, and it is, therefore, difficult to say whether they really 

 are Pelecypoda or not. They no doubt represent a special genus, of which FL 

 retifera is the type. 



Eichwald proposed for somewhat similar shells the name Ci/clostreon, which 

 I shall notice in the AuoDiiidce. 



Ic. Laube (Denksch. Akad., Wien, vol. xxv, pt. ii, p. 75,) describes from the 

 Trias of St. Cassian a peculiar smooth species, FL solea, which on one (? posterior) 

 side has a distant, double, lateral tooth near the margin. The valve described is 

 apparently the right one. The hinge-teeth are very close together, leaving only a 

 narrow groove for the ligament. It is probable that this species indicates a new 

 generic type. 



Species of FUcatula are known from the Trias upwards ; they are always found 

 in small numbers ; their largest development probably falls in the middle part of 

 the mesozoic period. At present there are only about twelve species known from 

 Eastern and American seas. 



2. Spondijlus, Klein, 1753, (Ostrac, p. 136, pi. ix, No. 37 ; Linne, 1757). 

 Valves very unequal, the lower, or right, more or less attached to foreign bodies, 

 with a flattened area between the beaks and the hinge ; upper valve smaller, with 

 distinct ears and a smaller, sometimes obsolete, hinge area ; hinge line generally 

 straight, more or less thickened ; hinge with a median, deep, usually well circum- 

 scribed, cartilage pit and a strong tooth on either side, with corresponding cavities 

 in the other valve ; muscular scar sub-central, large ; the inner portion of it is 



5 Q 



