OP SOUTHERN INDIA. 9 



I. Order. PHOLADACEA. 



This order includes burrowing Pelecypoda, provided with, a small foot, and with 

 long united siphons into which the gills are prolonged. The shells are small, cover- 

 ing only the anterior part of the body, while the posterior part often secretes a 

 calcareous tube, lining the cavity made by the animal. The ligament and cartilage, 

 as well as the hinge teeth, are generally obsolete, but sometimes there are present 

 long processes below the hinges for the attachment of muscles. Most of the species 

 burrow in solid objects, in wood and stones, or corals ; few in sand. 



The families belonging to this order are the Feoladid^ ( tebbbinin^ and 

 fkoladinm) and Oastroce^nijd^ (gastmocb^ninje, clavagellinjE^ and breceitin^). 

 Geologically, they are sparingly represented in palaeozoic strata, their number 

 gradually increasing in the meso- and kaino-zoic epochs, and they have their 

 maximum of development in the present time, possessing a wide geographical dis- 

 tribution, as regards genera as well as species. The most important monograph 

 of the recent species, belonging to this order, is that of G. Tryon, Junr., in the 

 Proceedings of the Philadelphia Academy of Natural Science. I shall have occa- 

 sion to refer to this paper frequently. 



I. Family,— FSOLADIB^, 



Animals club-shaped; the mantle closed anteriorly, provided with a single 

 perforation through which the more or less elongated, fleshy, and muscular foot is 

 protruded ; posteriorly the body is prolonged,— sometimes to a considerable extent,— 

 terminating with two more or less distinctly separated siphons. The posterior part 

 of the body is often covered with a shelly tube, while the anterior one is protected 

 by two equal or sub-equal valves, either gaping in front, or closed by a special shelly 

 lamina, and besides often strengthened exteriorly by small variously shaped, accessory 

 valves ; from the beaks extend internally towards the periphery one or more pro- 

 cesses, which are either free or grown to the valves, and to which the muscles of 

 the foot attach themselves ; there are no true hinge teeth present ; the pallial sinus 

 is always marked. 



Although the Pholads, — probably on account of the difficulty in collecting 

 them, — were for some time rather neglected by conchologists, they have received a 

 good deal of attention within the last few years. Later geological researches have 

 also brought to light a considerable number of fossil forms, so much so that in the 

 last decennium the number of known species has been more than doubled. 



It would be superfluous for me to enter here into any lengthened account on 

 the mode of life* of this group of Molluscs. Recent careful studies have suffi- 

 ciently proved that the enormous destruction which they produce on shipping and 

 submarine wooden-works is effected by a very simple mechanism. In the true 



^ I may mention on this subject Forbes' and Hanley's History of British MoUusca, Vol. I, p. 57, etc.,— 

 Deshayes' Paris fossils, Vol. I, p. 106, etc., and Fischer's studies on the Fholadid^ and TEREDwrn in the Journal 

 de Conchiliologie of 1857 and 1860. 







