MOLLUSCS. 



283 



Fig. 309. — Siliqita costata. 



before it has time to retreat. In Europe the clam-digger pours a little salt down the 

 hole ; this brings the clam to the surface, when it is quickly grasped. If not success- 

 ful, no subsequent salting will arouse the clam. Where the water is still, another 

 method is adopted. At loy tide the fisherman goes over the flats and puts a little oil 

 near each hole. When the tide rises and the clams come to the surface, this oil marks 

 the spots where they arfe, and thus the fisherman is readily guided to them. These 

 clams are said to be very good, but as to their merits compared with Mactra, Mya 

 Venus, and Ostrea, the writer can from his own ex- 

 perience say nothing. 



Siliqua costata is another common species on our 

 northeastern coasts. The shells are covered with a 

 greenish epidermis, which is enlivened by one or two 

 rays of more or less vivid violet. On the inside of the 

 shell is a thickened rib running outward from the umbo. 



This is one of the most common shells thrown up on sandy beaches, 

 and in life it is found buried in the sand a little below low-water 

 mark. Sol&myia velum is a very pretty shell, covered with a 

 light brown radiated epidermis which projects far beyond the edges 

 of the shell, its margins being slit into numerous lobes. The species 

 is active, leaping about with its foot, and swimming by opening and closing its valves. 

 A larger species is S. borealis, in which the lobes of the epidermis are proportionately 

 much longer and narrower. 



The filmily Gasteochjenidje, or Ttjbicolid^, has a very heterogeneous appear- 

 ance, some of its members bearing close resemblance to the next family. The shell is 

 equi-valve and the hinge is toothless, and not infrequently, in the adult, the shells are 

 imbedded in a calcareous tube, so that the whole has but little resemblance to an 

 ordinary bivalve. In Gastrochcena the valves are distinct from the tube, in Clavagdla 

 one valve is fixed, while in AspergiUum both valves are united with the tube, of which 

 they form a very inconsiderable portion, as is shown in our figure. All of the mem- 



FiG. 310. — Solemyia 

 velum. 



Fio, 311. — AspergiUum vaginiferuvi, watering-pot shell. 



bers of the family are borers, penetrating hard mud, shells, coral, or rock. The most 

 noticeable species is the ' watering pot,' AspergiUum vagini/erum. Here the valves 

 are very small, while the lower end of the tube is closed below by a disc, which is per- 

 forated by numerous holes and short tubules. The other part of the tube is much 

 longer, and at its distal portion i^ surrounded by one or more calcareous ruffles, so 

 that the whole has a very bizarre appearance. This sjjecies comes from the Red Sea, 

 and all other members of the genus belong to the Indo-Pacific region. 



The Pholadid^, taken in its widest sense, is a family chai-acterized by the absence of 

 hinge teeth and of hinge ligaments. Instead, we usually find one or two accessory pieces 

 (pallets they are called) which, in the Pholadinse, lie between the valves at the hinge 



