OP SOUTHEHN INDIA. 225 



more correct than the one adopted by H. and A. Adams, Chenn, or Deshayes, 

 but looking at the other peculiarities pointed out previously as regards the united 

 mantle margins, short foot, small labial palps, &c., and again the relations of the 

 shells to those of the Cramibm, the distinct grouping in the order CIIAMA CEA 

 appears to me to be best in accordance with our present knowledge of these shells. 

 The characters of the three genera are briefly as follows : — 



1. Verticordia, S. Wood, 1844. Shell sub^orbicular, equivalye, of small 

 size, moderately thickened, more or less inflated, with pointed incurved beaks, 

 surface with radiating ribs, sometimes besides ornamented with granules, covered 

 with a brown epidermis ; hinge with one small cardinal tooth in each valve below 

 the beaks, somewhat prolonged internally along the inner lunular edge, and in one 

 or the other valve this inner rim is occasionally interrupted so as to represent one 

 strictly cardinal and one sub-lunular tooth; the posterior edge of the shell 

 is generally occupied by a raised rim internally, which supports the internal linear 

 ligament. The type of the genus is V. ornata, d'Orb., and besides this four 

 other recent and four (tertiary) fossil species have been described, (vide Journ. de 

 ConchylioL, 1862, vol. x, p. 380). 



2. FeccMolia, Menegh., 1861, (vide Homes' foss. Moll, des tert. Beckens 

 von Wien, vol. ii, p. 168). Shell sub-orbicular, equivalve, strongly ventricose, with 

 the beaks incurved and distant from each other, surface radiately sulcated and 

 ribbed ; hinge in the right valve with a strong cardinal tooth below the umbo, a 

 corresponding indentation in the left valve ; ligament apparently linear, situated 

 along the upper posterior margin. 



The tooth of the right valve is supposed to have supported an internal carti- 

 lage, but there is no certain proof of this ; it in form greatly resembles that of a 

 Chama. On the whole, the character of the shell is that of a large solid Verticordia, 

 except that the left valve has no trace of a special tooth, and the posterior rim 

 for the support of the ligament is almost obsolete, but indicated by a groove in 

 the margin of the left valve. Only a single miocene species, P. argentea, is as 

 yet known. 



3. Allopagus, Stoliczka, 1870. fBippagus, apud Deshayes, non Lea, 

 Descript. des foss. du bas. de Paris, 2nd ed., vol. i, p. 809). Shell ovate, thin, 

 very inequilateral, moderately tumid, with small approximate beaks; surface 

 smooth with simple stride of increase ; right valve with one tooth in front of the 

 umbo, left with a similar tooth below the umbo ; ligament sub-internal, posterior. 

 The type of this genus is Sippagus Leanus, Deshayes, 1. cit., p. 810, pL 51, 

 figs. 1-3. The species differs by the hinge and the structure of its shell from 

 Sippagus, -- 'Lea.' s original figure of J2". isocardioides being apparently quite 

 correct,- the latter genus belonging to all appearance close to Mysia in the 

 Unqulinidm, Deshayes' species is externally very like a Mytilimeria, but this 

 again accords in the character of its hinge with true Sippagus, 



No cretaceous species of any of the Verticorbiii)^ have as yet been found, 

 nor are there any distinct indications of their occurrence in older deposits. 



