OP SOUTHEEN INDIA. 871 



12a, The former may be retained for a small number of species of the type 

 of Mod. pUcatula, Lam., with surface radiately striated and the anterior end 

 narrowed and obtuse, but it appears also to include a number of heterogeneous 

 species, some of which evidently are striated Mytili, and others seem to be more 

 correctly classed with Modiolaria, 



12b. Adula has been proposed for a single species, ^. 5oZem/6>rmi^, d' Orb., 

 a well marked solenoid form, thin, with sub-central beaks, like Myrina, a long 

 hinge line and with the posterior termination obliquely truncate. Carpenter 

 (in Ann. Mag. Nat. Hist., 3rd ser., xiv, p. 424,) suggests that the characters of thp 

 sub-genus be "enlarged to receive the shells of lithophagoid shape which are moored 

 by byssus, like ModiolaP The same author also says that Adula falcata, Gld., is 

 the largest species of the sub-genus, and lives in holes of clay together with 

 A. stylina and other boring shells. It is also suggested that Lithodomus parasi- 

 ticus^ Desh., and Lith, cinnamominus, Chem. fcinnamomeus, Brug.,) belong to 

 the same sub-genus. The latter species, I have already noticed, is closely allied 

 in form to Conrad's Arcoperna (seep. 369), although both are perhaps equally 

 correctly referable to the sub-genus JBotula, but I doubt the propriety of associat- 

 ing them with the typical species of Adula, Carpenter states in the characteristic 

 of Adula that the anterior part of the shell is the longer one, which seems incon- 

 sistent with the description of his new species and the figure of the type in 

 Chenu's Manual. 



Farther researches in the comparison of recent and fossil species and the 

 examination of the animals make it probable that a thorough reformation in the 

 generic and sub-generic groups of Modiola must sooner or later be carried out. 

 The materials are, however, as yet quite insufficient in order to make such a 

 re-arrangement really successful. 



13. Mytilus, Linn., 1758. Shell sub-trigonal, narrow, and more or less 

 pointed at the beaks, broader and generally rounded behind ; beaks terminal or very 

 nearly so ; hinge without distinct teeth, sometimes with one or two small tubercles, 

 and in the radiately striated species generally with a slightly crenulated margin ; 

 ligament partially attached on the internal side and supported by special fulcra, but 

 always also externally visible; muscular scars very unequal, the anterior being 

 much smaller than the posterior, which is often of irregular shape ; both are, how- 

 ever, rather indistinct, and so is also the simple pallial line ; type, Myt, edulis, Linn. 



136^. The name Mytilus^ has been restricted to the species provided with 

 smooth concentric strige of growth, sometimes also with a partially scabrous cuti- 

 cule. The radiately striated or ribbed species of the same type as M. Magellanious, 

 Chem., have been, according to H. and A. Adams, separated into a special sub- 

 genus under the name Aidacomya, They form but a subordinate section of the former. 



135. Stavelia has been suggested by Gray for Dunker's M, tortus and horri- 

 dm (see Proc. Zool. Soc, Lond., 1858, and An. Mag. Nat. Hist., 3rd ser., ii, p. 62). 



* Schlotheim applied to a number of fossil Mytilidm tlie name MytuUtes. 



4 X 



