LECTURES ON MOLLUSCA. 253 



chcera has a stout rib coming out at right angles from the beaks. The 

 mantle of the animal is beautifully fringed, and the pipes rather long. 

 The animal of the European Ceratisolen is very similar ; while the flat 

 narrow shell is drawn out nearly to the length of a Solen. All the 

 shells of this family gape, both at the foot and pipe ends ; and their 

 habits are like those of the Razor-fish. They do not make their ap- 

 pearance on our globe till the cretaceous age : the true Solens not till 

 the tertiaries. 



We now come to the typical Lamellibranchs, in which the pipes are 

 narrow in proportion to the animal, not swollen to allow of the entrance 

 of the gills. They are more or less united, or prolonged, in the va- 

 rious families and genera ; passing from the Tellens in some of which 

 they can be stretched out much longer than the shell, and widely 

 divergent, to the cockles in which they are united together, and scarcely 

 project beyond the valves. 



Family TELLiNiDiE. {Tellens.) 



The Tellens form a very beautiful and extensive family, abounding 

 on all shores, where they live in sand or mud, generally at slight 

 depths. The animals have very long, slender, and divergent pipes, 

 and large triangular lips. The mantle is elegantly fringed, and open 

 in front for the tongue-shaped foot. The shell is generally thin and 

 transverse, often highly colored and very delicately sculptured. 



In the first group, the shell gapes and forms a transition to the short 

 Solens. The shells of Soletellina are generally violet, with a somewhat 

 horny epidermis ; having small hinge-teeth, and beaked at the breath- 

 ing end. There is a strong ligament, supported on stout fulcrums. 

 In Sanguinolaria, the shell is shortened and very thin. Psammobia 

 gapes but little, and generally has the hinder side angular. In Cap- 

 sula the shell is swollen, and ornamented with radiating ribs. This 

 group makes its appearance in the cretaceous age. 



The typical group Tellina consists of shells varying from a very 

 transverse to a nearly rounded form, not gaping, and with a slight 

 fold or angle at the breathing end. The muscular impressions are 

 rounded and polished; and the mantle-bend is very large, occupying 

 a large proportion of the shell. In the Californian species, T. nasuta, 

 it is larger in one valve than in the other. The side teeth of the hinge 

 appear to be of very little consequence in this group, being sometimes 

 present in both valves, sometimes only in one, and often altogether 

 absent. About two hundred species are now living, and nearly a 

 hundred and fifty are found fossil, beginning with the oolites. The 

 orbicular species have been called Arcojxigia, a name also used unfor- 

 tunately for a group allied to JDonax. Some of the British, and 

 probably of the American species are said to have only two, instead of 

 four gills : they have been named Macoma. The Strigilla group, 

 which abound in tropical America, have rounded shells with the valves 

 obliquely sculptured. The elegant shells of Tellldora are found on 

 the east and west coasts of tropical North America ; they are white, 

 flat, and triangular, like Myodora. The shells of Gastrana are some- 



