Vol. VI, No. 5.] Chondrodonta Bosei. 257 



[N.S.] 



After 



me 



■*- i M* * 



I have much pleasure in dedicating to my distinguished informer. 



The species may be defined as follows : large, elongate- 

 triangular, greatly compressed, with undulating almost flat 

 valves, of which the upper one often shows a tendency to become 

 concave ; both valves similarly decorated with uniformly crowd- 

 ed excessively fine angular ribs increasing by dichotomy with 

 the increase in size of the shell. 



The dimensions ] of the figured specimen are about 160 mm. 

 in height, 118 in length, and 20 mm. to 30 mm. in thickness. 

 In another larger specimen, the approximate dimensions are 

 respectively 175 mm., 129 mm., and 25 to 35 mm. 



All the specimens have the valves united. Judging from 

 fractured examples the hinge plate seems relatively much 

 shorter than in Chondrodonta Joannce, Choffat, and Ch. Munsoni, 

 (Hill) Stanton. These species differ from the Seistan form 

 by their distinctly coarser sculpture. The form from northern 

 Italy described by Boehm % as Ostrea aff. 0. Munsoni and by 

 Fiitterer 3 as Pinna ostraeiformis seems more nearly related, 

 though, even in this case, the ornamentation still remains some- 

 what coarser. The occurrence of the ribs varies somewhat 

 in the Seistan specimens, and is in some cases coarser toward 

 the umbo than near the margin, but still it always remains finer 

 than in the Alpine fossils even in the most extreme cases. 



The nearest relative to C. Bosei appears to be the form 

 described by Choffat as Ostrea Delgadoi (Faune Cretacique du 

 Portugal, i, p. 36, pi. hi, figs. 1 and 2), which does not seem 

 to have been included by Stanton in the genus Chondrodonta, 

 though referred by Choffat to the group of " Ostrea Joannce.' 9 

 The ornamentation appears to be absolutely identical with that 

 of the Asiatic species, only the size is much smaller. The shape 

 of the shell is less elongate than in the full-grown specimens 

 from Seistan, but this is a character which cannot be depended 

 on in shells of such variable shape. Judging by the sections 

 across the valves published by Choffat , the hinge- plate in Chondro- 

 donta Delgadoi also seems relatively short, constituting another 

 point of resemblance with the Asiatic form. Should specimens 



unite C. Bosei with C. Delgadoi. 



When first mentioning thi 



of India, xxxviii, p. 223), I si 



necessary 



*> 



I I am indebted to Bankim B. Gupta. Museum Assistant, for 



measuring the specimens. 



* Beitrage zur Kenntniss der Kreide in den Siidalpen. I Die 

 Schiosi-und Calloneghe- Fauna, Palceontographica xli, 1894, p. 06, pL 



viii, figs. 1,2. 



8 Palceont. AbhandL. Dames und Kayser, vi (new .series), ii, 1896. 



pt. 2. p. 259. 



