308 " THETIS " SCIENTIFIC RESULTS, 



material on hand, we agree that the minute sculpture of the recent 

 species divides it from the fossil, but in view of the variability of each 

 we regard it as probable that a larger series might bridge the gap. 

 Mr. Etheridge has kindly drawn up the following detailed com- 

 parison : — 



" The outline and auricles, cardinal margins, chondrophore, 

 latilaminte and adductor impressions in each valve are the same 

 in both fossil and recent forms 



Right valves. — The fasciculate primary costte in both are six in 

 number and rounded. In the recent form the fasciculi are flat, 

 entire and depressed, and are differentiated from one another by 

 faint grooves. In the fossil shell the fasciculi are sharp, each 

 distinctly separated from its neighbours and bifurcate. 



The intercostal spaces in the recent shell are traversed by 

 simple secondary narrow costfe. In the fossil these second costse 

 are similar to the fasciculi of the primaries, and are more numerous 

 than the secondaries of the recent form. 



The sculpture of the recent shell consists of almost microscopic, 

 remarkably close, concentric, scobinate frills on the intercostal 

 spaces, reduced to ordinary linear sculpture on the primary cost*. 

 In the fossil the whole of the fasciculi are sub-echinate, and on 

 the anterior end echinate, whilst the intercostal spaces exhibit 

 concentric frills only. 



Left valves. — -Primary costse are 6, prominent, of indefinite 

 fascicules, except on the anterior and posterior ends, and are of 

 less width than the intercostal spaces. In the fossil they Tnay be 

 6 and depressed, but the component fascicules sharp. 



The intercostal spaces in the recent form bear secondary cost*, 

 which are obliterated by upstanding concentric frills passing 

 equally and uniformly across them and the primary costiie. The 

 fossil apjaears to have possessed the same sculpture." 



From 19-20 fathoms in the vShoalhayen Bight. 



DIMYA, Roitalt. 



DIMYA CORRUGATA, sp. nov. 



(Fig. .52.) 



(Station 49. 



Shell irregularly trapezoidal, higher than long, obliquely pos- 

 teriorly produced, both valves shallow, the left or free valve the 

 Hatter. In the shade the surface is dull grey, but in reflected 

 light it has a brilliant silvery sheen. Sculpture: close fine 

 concentric growtli lines in the early stages are distorted by 



