OP SOUTHEEN INDIA. 335 



fig. 17,) describes the same species from corresponding rocks of N. Wales. Accord- 

 ing to his figure the hinge area is rather broad and instructed with seven elongated 

 ribs, diverging in a semicircle, indicating a peculiarity of the hinge distinct 

 from any other genus of the Arcidje, Consequently the other species referred by 

 Hall to the same genus, i. pulchella (ibidem, p. 302,) is generically different from 

 the former, as was suspected by that author ; it may perhaps belong to Gtenodonta, 

 Another species of Lyrodesma is, however, Nuculites poststriata, Emmons, (Hall, 

 1. cit., p. 151 and p. 301). Judging from the above characters, the only known forms 

 allied to Lyrodesma are those of the recent Cyrilla and the tertiary Trigonoccelia. 

 Lyrodesma would seem to connect the axwmin^ with the arcing. 



b. Sul-family ^-—ARCINM. 



1. Cardiola, Broderip, 1834, fvide Sandberger, Rhein. Schichtensystem 

 in Nassau, 1850-56, p. 269). Shell somewhat inequilateral or sub-equilateral, 

 roundly ovate, with the beaks incurved anteriorly and with a rather large liga- 

 mental area between both ; hinge line slightly curved with numerous oblique plici- 

 form teeth, being apparently present on both sides of the beak ; surface generally 

 radiately striated or ribbed; type, C. retrostriata, Buch. All the species are from 

 palaeozoic beds ; their hinge-teeth have as yet been only partially traced, and the 

 characteristic of the genus is therefore unsatisfactory. In some species the hinge- 

 teeth appear to be similarly disposed as in Lyrodesma, in others they seem to be 

 similar to those of Cypricardites. Much better materials than those now on 

 record are required for a proper definition of Cardiola ; in external form it mostly 

 recalls the recent Argina and Lunar ca of Gray. 



2. Cypricardites, Con., 1841, (Palsearca, Hall, 1858, Pal., New York, vol. iii, 

 pp.271 and h'^Z, Gyrtodonta, Billings, et F■c^7^^^<?mm apud Billings, ex parte)* 

 Shell elongately or roundly ovate, tumid, inequilateral, the beaks being almost 

 anterior and incurved; hinge area narrow or sometimes apparently almost 

 obsolete ; hinge line rather straight, with a few (usually 4-6) short oblique teeth 

 in front and sometimes near the umbones, and a few (1-4) elongated nearly 

 horizontal teeth at the posterior end; type, Cyp, ventricosa. Hall. All the species 

 appear to be confined to the palaeozoic rocks. The character of the hinge-teeth 

 of Cypricardites shows relations to Macrodon, and the former may be considered as 

 the predecessor of the latter in geological history. Probably some of the species 

 described as ' Cypricardia' from the Devonian and Permian rocks belong to the 

 present genus. 



3. Bahewellia, King, 1848, (Perm. foss. of England, &c., 1850, p. 166). 

 The form of the shell of this genus is very similar to Cypricardites, except that the 

 posterior upper edge is somewhat more expanded, wing-like, the shell, therefore, 

 closely resembling a small Avicula ; the hinge area is broad, and the ligament 

 apparently situated in several obliquely transverse grooves, hinge line straight, 

 internally with a few short, oblique anterior, and 1-3 nearly horizontal, elongated 

 posterior teeth, as in Cypricardites ; type, Mytilites ceratophagus, Schlotheim. It 



4 N 



