28o JOURNAL OF CONCHOLOGY, VOL. II, NO. 9, JANUARY, I906. 



from the types of the connected species than these do from one 

 another. 



It seems to me that we have an illustration of this in the case of 

 Tapes rhomboides {==virgineus Auct.) and the T. aureus group. The 

 former differs from the latter chiefly in its rhomboidal shape, in hav- 

 ing fewer concentric grooves, and a less defined lunule. Now it 

 appears to me that a typical T. texturatus differs quite as much from 

 T. aureus as the latter does from T. rhomboides ; and that if the last 

 is regarded as a good distinct species, so also should texturatus and 

 catenifer in spite of the links which connect them with aureus. 



I am not sure, however, that T. rhomboides is an isolated species. 

 Like T. aureus, it is local in the Mediterranean, but the var. pulchella 

 has by some authors been grouped under T. aureus, and must there- 

 fore be a kind of link between them. Again, the author of T. elongatus 

 places it under T. aureus, but it has almost as much resemblance to 

 T. rhomboides. 



I should, therefore, arrange the species above mentioned and their 

 principal varieties as follows : — 



I. Tapes rhomboides Penn., with vars. curta zxvdi pulchella. 

 2.? Tapes elongatus B.D.D. 



3. Tapes aureus Gmelin, with vars. ovata, quadrata, and rugata. 



4. Tapes catenifer Lam., with vars. bicolor, petalina, bourguig- 



nati, grangeri, and others. 



5. Tapes texturatus Lam., with vars. mabillei, nitidosa, rostrata, 



retorta, and others. 



The history of this group of species seems to be that they all sprang 

 from a common ancestor in Miocene times, that they became differen- 

 tiated in early Pliocene times. T. rhomboides and T aureus seem to 

 have attained their chief development in the colder seas ; both are 

 found fossil in the newer Pliocenes of England, and exist now in the 

 North Sea and on the coasts of the Atlantic as far south as the Straits 

 of Gibraltar. It is an interesting fact that T. aureus is very rare in 

 the western basin of the Mediterranean, but exists in the eastern 

 basin. M. Dautzenberg informs me that he has a specimen from 

 Venice and three typical specimens from Greece, besides the variety 

 from the Bosphorus ; according to Middendorf, it also exists in the 

 Black Sea. Tapes rhomboides seems to have been more abundant in 

 the Mediterranean area during Pliocene times than it is now in that 

 sea, having been recorded from the Pliocene deposits of Italy, Sicily, 

 Rhodes, and Cos. On the other hand. Tapes aureus does not seem 

 to occur in these deposits. 



As T. elongatus is also confined to the eastern basin of the Mediter- 

 ranean, one may infer that it has been developed from one of these 



