256 Journal of the Asiatic Society of Bengal* [May, 1910. 



To this cause is due no doubt the sudden disappearance, 

 at the end of the secondary, of the curious mollusca here referred 

 to. Some of these singular shells belong to the extinct family 

 of the Rudistce of which the most familiar type is represented 

 by the large shells known as Hippurites. Curiously enough 

 there has not been so far a single specimen of a genuine Hip- 

 purite discovered within the present limits of the Indian Empire, 

 though certain closely related genera, especially Radiolites, are 

 frequent amongst the deposits of the age of the great banks of 

 Rudistce. In one of the lately published numbers of the Records 

 of the Geological Survey of India (xxxviii, pt. 3), I gave descrip- 

 tions of two species of genuine Hippurites which were discovered 

 quite close to the Indian frontier, in Seistan. 



A close study of the Rudistse banks constantly reveals the 

 presence of abnormal organisms in which the original characters 

 are not disguised to such an extent as in the Rudistce themselves, 

 though they are apt to assume a very exceptional appearance. 

 In the case of the Seistan deposits, the hippurites are accom- 

 panied by large numbers of a singular bivalve which I was unable 

 to refer to any genus with which I was then acquainted. I 

 published a photograph of this curious organism, and, thanks 

 to the courtsey of Dr. Emil Bose of Mexico, I am now able to 

 give a name to this fossil. 



The following is Dr. Emil Bose's communication dated 

 Mexico den 30 January, 1910. 



1 ' In Hirer letzen Publikation in den Records der Geol. Survey 

 bilden Sie eine Bivalve ab, von der Ihnen das Genus unbekannt 

 ist. Der Abbildung nach zu schliessen, durfte es sich wohl urn 

 eine Chondrodonta ahnlich der Chondrodonta Munsoni Hill 

 handeln, die in den Ver. Staaten im Gaultvorkemmen soil, 

 hier in Mexico findet sich eine verwandte species in Cenoman, 

 in Europa kommt die Chondrodonta Joannce im Turon, aber 

 nach Schnarrenberger audi Vorcenoman vor. Sie finden einen 

 Theil der betreffenden Litteratur in der Arbeit Stanton's 

 " Chondrodonta, a new genus of ostreiform mollusks from the 

 cretaceous, with descriptions of the Genotype and a new species ' 

 (Proc. U. S. National Museum, xxiv, p. 130-307)- Nicht erwahnt 

 ist darin Z.B. die Publikationen von R. Hoernes iiber Ostrea 

 Joannce, dis Sie aber leicht finden werden. 



. In der Hoffnung, dass Ihnen diese Angaben von Nutzen 

 sein werden verbleibe ich mit dem Ausdrucke grosster Hochach- 

 tung. ' * 



Amongst the specimens from Seistan there are several in 

 which the hinge is slightly damaged in such a manner as to 

 show the peculiar interlocking chondrophores characteristic 

 of the genus established by Stanton in the work above alluded 

 to by Dr. Bose, and thereby confirming Dr. Bose's attribution. 

 They can be distinguished in the particular specimen already 

 illustrated in the Records of the Geological Survey. 



