East coast marine shells; descriptions of shore mollusks together with many living below tide mark, from Maine to Texas inclusive, especially Florida eastcoastmarines00rome Year: 1937 often heart-shaped, indented space in front of, or anterior to, the umbones. Fig. 21. In separated valves this space is called the ANTERIOR SINUS but it is present in both valves. Many species do not possess the lunule. Fig. 21 The Hinge and Its Lunule, heart- Parts. The active bivalves shaped area usually have the strongest hinges; the sluggish forms, or those which are fixed during life, the weak- ly formed o
East coast marine shells; descriptions of shore mollusks together with many living below tide mark, from Maine to Texas inclusive, especially Florida eastcoastmarines00rome Year: 1937 often heart-shaped, indented space in front of, or anterior to, the umbones. Fig. 21. In separated valves this space is called the ANTERIOR SINUS but it is present in both valves. Many species do not possess the lunule. Fig. 21 The Hinge and Its Lunule, heart- Parts. The active bivalves shaped area usually have the strongest hinges; the sluggish forms, or those which are fixed during life, the weak- ly formed or toothless ones. The hinge itself is on the margin and composed of chitinous ligament and teeth (denticles) which closely interlock. There is great variation among the HINGE TEETH. Juveniles show well-defined characters and are better for study. Old individuals often partially cover the teeth with shell deposit and they are consequent- ly ill defined. The CARITNAL TEETH are placed immediately below or between the um- bones. Fig. 19h. On each side of the cen- tral teeth, or cardinals, are the LATERAL TEETH which often are well apart from the others. The ANTERIOR-LATERAL, Fig. 19J, is the one in front of the shell, while the POSTERIOR-LATERAL, Fig. 19k is the one in the rear. While the cardinals are some- times very small, or absent altogether, it is more frequent to find the lateral teeth not present. In Area the usual teeth are lacking and are replaced with a large num- ber of regularly arranged small teeth. The latter are usually feeble toward the umbo. The hinge of Cardium is shown in Fig. 22. All sorts of com- binations and develop- ments occur among the hinge teeth. Upon these depend, to a large ex- tent, the identifications of many species. Fig. 22 Hinge of Cardium, exhibiting arched teeth locomotive and organism. The as the ADDUCTOR DUCTOR is shown ADDUCTOR in Fig The Muscular Im- pressions. These indenta- tions inside bivalves often indicate the condi- tion and posit
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