SMITH ON THE AGE OF THE TERTIAR^iT BEDS OF THE TAGUS. 417 



Descrijptio7is of Figures, Plates XV.-XX., hy Mr. G. B. Sowerby. 



Pholas altior. 



Fig. 1. 



Ph. testa ovato-oblonga, antice rotuudata, lineis incrementi rugulosa, costellis 

 radiantibus circa 18, distantibus, lineas incrementi decussantibus ; postice Isevi ; 

 margine dorsali declivi. Long. 3*4, lat. 1-5, alt. 1*6 poll. 



This species, as far as we can judge from a single imperfect speci- 

 men, comes nearest in its characters to Pholas Candida ; it differs 

 however greatly in its proportions, and also in the circumstance of its 

 posterior part being free from the radiating ribs, which cover about 

 two-thirds of this shell, while the Ph. Candida is entirely covered 

 with them. It is not without some hesitation that we place this shell 

 among the Pholades ; still we think the balance of evidence is in 

 favour of our decision. 



Artemis elliptica. 



Figs. 2, 3. 



Art. testa subelliptica, rotiindato-subtrigonali, tumidiuscula, insequilaterali, latere 

 antico brevi, subrostrato, margine dorsali antico, rectiusculo, declivi; latere 

 postico longiore, postice subtruncato, margine dorsali rotundato-subdeclivi ; 

 lunula magna, ovali, linea tenuiter impressa circumscripta ; margine ventrali 

 rotundato ; superficie Iseviuscula, lineis incrementi concentricis acutis soliim 

 insculpta. Long. 2*5, lat. 1-4, alt. 2*1 poll. 



The general form of this species, being similar to that of many 

 Cytherea, would, at a first sight, have induced us to place it in that 

 genus : the characters of its hinge, with the fulcrum, to which the 

 cartilage is attached, eroded close to the umbones (as in Cyprind), 

 and those of the muscular impressions, compel us to unite it to Artemis : 

 it is principally in its more elliptical form that it differs from the other 

 species of that genus. This species resembles greatly, and is certainly 

 congeneric with, Venus Brocchii of Bronn (which is put into Cyprina 

 by most authors), but which is nearer to Artemis than to Cytherea, 

 Venus or Cyprina. 



Cardium pholadiforme. 



Figs. 6, 7. 



Card, testa oblonga, tumidiuscula, antic6 obtusa, subrotundata, postice subat- 

 tenuata, umbone magno, costis radiantibus circa 10, magnis; impressione mus- 

 culari postica circular!, profunde impressa. Long. 1*9, lat. 0'9, alt. 1'15 poll. 



Of this species we have only a single cast of the inside ; it is com- 

 posed of a greenish-grey-coloured fine sand, with very small remains 

 of the shell. 



Cardium latisulcatum. 



Figs. 4, 5. 



Card, testa subglobosa, subsequilaterali, costis radiantibus circa 18, iuterstitiis 

 duplo latioribus. Long. 1*5, lat. 1*3, alt. 1*6 poll. 



Casts of the inside alone have been found of this species ; it is 

 therefore obviously impossible that we should give the external cha- 



