LECTURES ON MOLLUSCA. ] 07 



species to California ; although the west coast of North America has 

 not yet furnished a single shell belonging to this sub-family. The 

 shells of Anapa are shaped like Erycina, but there is no mantle-bend, 

 'and the animal may prove to be allied to Crassatella. The shells of 

 Ervillia belong to the Atlantic ocean and the Red Sea. They have a 

 Tellinoid shape, with deep mantle-bend, but no lateral teeth. Shells 

 of this section have been found fossil in the earlier cretaceous age. 



Family MACTRID^E. 



The beautiful shells of this family are generally somewhat trian- 

 gular, and witlj. an internal cartilage, like Erycina: but the breath- 

 ing-pipes are united to the end, and beautifully fringed The mantle 

 is freely opened in front, allowing free play to the tongue-shaped foot, 

 which is used either for burrowing in sand or for leaping. The lips 

 are very long and pointed. The shells are generally thin, and often 

 highly colored. Mactra proper has well developed lateral teeth, double 

 in one valve, and a small ligament separated from the cartilage. 

 Spisula has the side teeth strong and cross-ribbed, as in Ceronia. The 

 American genus Mulinia has the ligament internal as well as the car- 

 tilage ; the side teeth smooth, and the mantle-bend angulated. In 

 the African form Schizodesma, there is a triangular opening between 

 the beaks to receive the ligament. Mactrella is a tropical American 

 group ; with very thin shells, keeled on one side and gaping at each 

 end. The side teeth are very short, and the mantle-bend large and 

 round. Harvella is another tropical American form, with paper-like 

 shells, keeled on one side and concentrically furrowed. The ligament 

 is separated from the cartilage. In Standella it is joined to the carti- 

 lage, as in Spisula y and the side teeth are short, not projecting beyond 

 the cartilage pit.* All the strictly marine Mactrids have a V-shaped 

 hinge tooth, more or less devel^bed. They are found fossil in all 

 strata from the Lias. Another tropical American group, Bangia, (bet- 

 ter known as GnatJiodon,) inhabits brackish water, and has the breath- 

 ing-pipes partly separated. Though the shell is angular, the hinge 

 line is rounded, and the V-shaped tooth is broken into two. Though 

 the shells are so abundant near New Orleans and Mobile as to be used 

 for making roads, they are still sadly too rare in Europe. 



Another somewhat aberrant group may, from the shells alone, be 

 grouped either with the Lutrarias or Madras. Their true position 

 cannot yet be determined, through our ignorance of the animals. The 

 liaeta, so abundant in South Carolina, but rare in Europe is like Har- 

 vella, with the side teeth changed into clavicles supporting the hinge 

 plate. Cypricia (unfortunately confounded by Messrs. Adams with 

 Cryptodon of Conrad) is a closely related form, not furrowed, and 

 largely gaping in front. The mantle-bend in both groups is more 

 akin to Lutraria than to Mactra. In Heterocardia it is very large, 

 as in the Tellens, and the hinge somewhat resembles Eangia. The 

 shells of CcBcella inhabit shallow muddy bays. They have a mantle- 

 bend like Mactra, with a hinge like Lutraria. The very singular 



*This genus will probably be found more nearly related to Luhraria. 



