OP SOUTHERN INDIA. 65 



16. Lyonsia^ Turton, 1822, (Magdala, Leach). Shell more or less inequi- 

 lateral, ovate, somewhat gaping posteriorly and often distorted, nacreous inside ; 

 hinge with an oblique and marginal cartilage groove in each valve behind the beaks, 

 cartilage covered in front with a flat oblong ossicle. There are numerous palaeozoic 

 and mesozoic fossil species which probably will have to be referred to this genus ; 

 from the tertiary period about 12 are known, and 15 recent ones are recorded by 

 Conrad in his catalogue of the Anatinibm, Deshayes (Paris foss., 2nd edit., 

 pp. 257-258,) argues at length whether it be desirable to distinguish generically 

 between Lyonsia and his Osteodesma, He states that there are some species which 

 are nearly equilateral, of regular form, and with very unequal valves ; others which 

 are irregular, less inequivalve, and very unequilateral. The former, he suggests, 

 could be called Lyonsia, the latter Osteodesma. This distinction is, however, by no 

 means constant, and scarcely of sub-generic or sectional importance. Deshayes 

 himself, immediately after this discussion, describes two species, Ly, Seberti and 

 plicata, representing the two forms under the single generic name Lyonsia ! 



17. Lyonsiella, Sars, 1868. I only know this name from the quotation in 

 Ann. Mag. Nat. Hist., 4th Ser., vol. iv, p. 429; it is based upon a northern form, 

 L. abyssicola, evidently allied to Lyonsia, and found in 450 fathoms ; the author 

 promised soon to supply a description in the " Vidensk.-Selskabs Porhandlinger." 

 Perhaps he did so before his lamented death. 



18. LJntodesmas Thiliipi^i, 1845, may be distinguished generically, because 

 the form of the shell is almost like that of a Modiola, or Saxicava, with an internal 

 semicircular cartilage process; the ossicle and pallial impression have not been 

 observed. B, Chiloensis is the type. The form of the shell appears to indicate a 

 passage to Mytilime^'ia, 



c. Biih-family,—ANATimNM. 



Most of the shells referred to this sub-family have a very thin nacreous, some- 

 times nearly membranaceous shell, of an oval or elongated form, generally gaping 

 at the posterior end. By far the larger number of forms are fossil, and of the few 

 recent species known the animals are characterized by long united siphons covered 

 with an extension of the more or less hardened epidermis of the shell. 



The classification of the anatininm is as yet very unsatisfactorily known. 

 Some forms are very tumid and of a cordate shape, like the recent Mytilimerice, 

 or the fossil CeromycB, and others are elongated and sometimes considerably 

 compressed, as the typical Anatincs and the fossil Corimyce. But when we look, 

 for instance, upon the enormous number of known Fholadomyce, we meet similar 

 variations in one and the same genus. To avoid, therefore, great confusion I have 

 attempted to associate as much as possible the fossil forms with their nearest allies 

 among recent shells. The fossil genus Bibeira is by some palaeontologists referred to 

 the Anatinidm, but Salter considered it to be more allied to the JEstherice, and 

 that appears probable. 



B 



