56 



l-estricted, and as the type of Parapholas has only one, the Queen 

 Charlotte Island fossil is, for the present, regarded as a Martesia. It 

 is not improbable that the two genera will ultimately be merged in 

 one, and in that case Martesia, which is much the oldest name, will 

 have to be retained. 



Martesia tundens of Stoliczka, from the Cretaceous rocks of Southern 

 India, in its young state nearly resembles the present species, but the 

 Asiatic shell is more elongated and acute behind, and its valves are 

 marked by only one impressed groove. 



Thracia (Sp. undt.) 



Compare Lutraria (Thracia ?) carinifera, Sowerby. •' Mineral Concliology, " Vol. VI., 

 p. 66, Plate DXXXIV, fig. 2. (^Lyousia (? Thracia) carinifera, (Sow.) D'Orbigny. 

 " Paleontologie Fran^aise, Terrains Cretaces," Vol. III., page 385. Atlas, Plate 

 CCCLXXIIL, figs. 1 and 2. 



A single imperfect cast, with the surface much abraded, which clearly 

 belongs to the same genus as the fossil with which it has just been com- 

 pared, and is very much like it specifically. Both are squarely truncate 

 behind ; in each there is an oblique ridge or keel which extends from the 

 beaks to the posterior end of the base ; and there is a certain resemblance 

 in the general outline of both. Still, the two S2)ecies are entirely distinct; 

 the beaks in Mr. Eichardson's specimen are divergent and wide ajiart, 

 they are placed also at a considerable distance behind the middle, and 

 consequently the shell is produced anteriorly and very short posteriorly. 

 In Thracia carinifera the beaks are close together and nearly central, 

 while the length of the shell is greater in proportion to its height than is 

 the case with the species from the North Pacific. The only specimen of 

 the latter is too imperfectly preserved either to permit of a sufficiently 

 accurate description being made, or for a satisfactory comparison with 

 closely allied forms. 



Agassiz places Sowerby's Lutraria carinifera in the genus Corimya, but 

 Stoliczka, who favours keeping Corimya and Thracia. apart, thinks that it 

 may be a Thracia, although he previously states that " fossil species be- 

 longing to Thracia proper are as yet only known from Tertiary deposits ; 

 those from Cretaceous beds may, with equal probability, be referred to the 

 former genus " (^Corimya). Pictet states more positively that it is a 

 Thracia. 



