166 Prof. E. Forbes on Fossil Invertebrata from Southern India. 



nites and Terebratula, and the several genera of Cephalopoda and Echinida, are 

 familiar examples. The inestimable researches of Von Buch have, above all others, 

 furnished us with this invaluable key to the ages of deposits, one which will as- 

 suredly prove in the end of far greater importance than the identification of strata 

 by identical fossils. In the collections before us there are fortunately numerous 

 forms, above all others capable of furnishing us with such a clue to the age of the 

 beds. The fossil Cephalopods, so beautifully preserved in this collection, are so 

 numerous and so varied that they alone might settle the question. Twenty-one 

 out of twenty-eight well-marked Ammonites belong to sections of that great genus, 

 pre-eminently and characteristically cretaceous, and of the seven remaining, five 

 are the near allies of cretaceous forms. The Hamites, Baculites and Ptychoceras all 

 have similar relations. The Gasteropoda, though at first sight more like tertiary 

 than cretaceous forms, include many very nearly allied to known upper and lower 

 greensand species. The Pleurotomarice of the collection are peculiarly cretaceous. 

 The genera Tornatella, Strombus, Rostellaria, Murex, Pyrula, Vermetus and Nerita, 

 though the association of them appears tertiary, have all representatives in the 

 cretaceous strata of Europe, and some in older rocks. Voluta itself, the genus 

 which contributes most to the tertiary aspect of the collection, has representatives, 

 and those not peculiar forms, as low down as the upper greensand in Europe, 

 and occurs also in cretaceous strata in North America. Turritella, Cerithium, 

 Dentalium and Trochus are genera represented in more ancient formations, 

 and, owing to the peculiarities of their sculpture, as likely to present resem- 

 blances to recent forms in the oldest beds as in the newest. Chemnitzia, Scalaria, 

 Eulima, Ringicula and Natica are genera having no greater weight in the 

 argument for similar reasons, or else on account of their fossil relations being 

 at present insufficiently known. There are three genera however among the 

 Pondicherry Gasteropoda hitherto unrepresented in formations older than the 

 tertiary epoch : these are Cyprcca, Oliva and Calyptraa. The determination of the 

 last is doubtful, but the species of the two former certainly have their nearest allies 

 among tertiary and recent forms. 



Every genus of bivalve testacea in the collection is already known in cretaceous 

 strata or older. The peculiar forms of Cardium, Area, Trigonia, Mytilus, Phola- 

 domya and Grypha;a, all genera presenting subdivisions remarkably limited in their 

 distribution in time, are characteristically cretaceous. The species of Panopaa, 

 Anatina, Pectunculus, Nucula, Lima, Pecten, Plicatula, Clavagella and Solecurtus 

 are all most nearly related to described European cretaceous forms of those genera. 

 The tertiary aspect of the Trinchinopoly beds is derived from the presence of nu- 

 merous bivalves recalling recent forms, but really more from their state of pre- 

 servation than from being more nearly alUed to recent shells than cretaceous 



