MOLLUSCS. 



283 



■ .Siliqua costata. 



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

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

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

 method is adopted. At low 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 are, and thus the fisherman is readily guided to them. These 

 clams are said to be very good, but as to their merits comi)ared with Maclru, Mya 

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

 perience say nothing. 



Siliqua custata is another comniun 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 

 slicll i^ 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. Solemyia 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 numerotis 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 family GASTROrii.ENiD^, or TuBicoLiD.t;, has a very heterogeneous appear- 

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

 eipii-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 Gastrochceiia the valves are distinct from the tube, in Clavagella 

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

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



FlG. 311. — Aspergill 



watering-pot shell. 



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

 noticeable species is the ' watering pot,' Asperyillum iHfffiHiferum. Here the valves 

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

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

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

 lliat the whole has a very bizarre apjiearance. This species comes from the Red Sea, 

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



The PnoLADin.E, taken in its widest sense, is a family characterized by the absence of 

 hinge teeth and of hinge ligaments. Instca<l, we usually find one or two accessory pieces 

 (pallets they arc called) wliich, in the Pholadiiue, lie between the valves at the hinge 



