48 TEE ZOOLOGIST. 



as a matter of fact, by far the commonest position is a more or 

 less oblique one with the ventral border superior. Of the eleven 

 hammered shells included in the general total, ten were opened 

 through the dorsal border, and only one through the ventral. 



Owing to the great development of soft epidermis in the 

 growing Modiola as compared with the thin covering of Mytilus, 

 it is possible in a large number of shells to see, from the marks 

 made by the pressure of the bill, where the bill was introduced 

 between the valves. The study of these impressions confirms 

 the results obtained more or less indirectly from Mytilus. When 

 the bill is pushed into the shell through the dorsal border and 

 leverage is applied, one valve splits along a curved line extend- 

 ing from a point near the posterior end of the hinge to the 

 anterior end. When the bill is introduced through the ventral 

 hiatus, no fracture is caused, as a rule, and if one does occur it 

 runs transversely across the shell, or more rarely it takes a 

 quadrangular form. In one of the shells opened by the thrust- 

 ing method, the bill, after being pushed into the shell through 

 the hiatus in the ventral border, had perforated a worn part of 

 the shell an eighth of an inch obliquely behind the posterior 

 end of the hinge ; in another case entered similarly, the bill had 

 been pushed through the dorsal cleft just behind the hinge, 

 causing comminution and eversion of the edges of the valves at 

 that point. In two of the hammered shells the blows had been 

 delivered so evenly between the two valves in each case that a 

 semi-ellipse of each valve had been driven inwards before the 

 bill. As it happened, one shell had been attacked at the 

 summit of the dorsal border, and the other through the hiatus 

 in the ventral border. 



Tapes pullastka. 



The shells of Tapes pullastra are found in the same localities 

 as are those of the Horse Mussel. But, in comparison with the 

 latter, the Tapes are much better hidden from sight under vege- 

 tation, in sandy concretions, or in colonies of Mytilus, while a 

 proportion of them resides in the holes made by rock-boring 

 molluscs. The Oystercatcher discovers the shells by a laborious 

 process of inspecting and probing the materials in which they 

 are imbedded, and having found a shell it has usually no difficulty 

 in gaining admission, owing to the great protrusion and slow 



