OP SOUTHERN INDIA. 259 



specimens very strongly dentated and thickened. I have only imperfectly seen 

 the hinge-teeth, the cardinals appear to be regular, the posterior are very much 

 smaller than the anterior ; on each side there is a long lateral rim parallel to the 

 margin, as in other LucincB, but whether it terminates with a special lateral tooth 

 I have not been able to trace out. 



Localities. — Olapaudy and west of Arrialoor, in a brownish and grey conglo- 

 meratic sandstone. 



Fo7ination, — Arrialoor group. 



XXIV. Family,— UNGULINID^. 



The animals of the genera referable to this family agree in form with those of 

 the LuciNiDM, but they have the mantle margins much more united below, leavino- 

 in front only a comparatively small pedal opening, the siphonal orifice is also sino'le ; 

 the gills are of moderate size and consist of two elongated plumes on each side ; 

 the foot is elongated, hollow inside, generally vermiform, or somewhat geniculate, 

 but always much shorter than in the previous family ; the mouth is of moderate 

 size, and the palpi, four in number, well developed. 



The shells are oval or roundish, rather thin, with the internal surface always 

 of a peculiar silky or pearly appearance and mostly quite smooth ; the hinge usuallv 

 has two small cardinal teeth in each valve, the laterals are always wanting ; the 

 muscular scars are oval, or elongately oval, sub-equal, the anterior being rarely 

 much longer than the posterior ; pallial line entire, sometimes truncate posteriorly 

 and generally faint ; ligament external or sub-internal. 



I shall refer to this family the following seven genera : Sippagus, Scacchia, 

 Ungulina, Cyrenoida (^=Cyrenella), Felania, Mysia C=Diplodonta), and FsatMira. 

 Deshayes, and many other conchologists who accept that celebrated author's 

 views, class several of the above-named genera in the Lucinidm, admittino* the 

 difficulty which exists in the classification of the fossil species. There can be no 

 question that all those genera quoted exhibit a very marked relation to the i?7c/ivjz>^ • 

 but when we look at the important differences which I have pointed out in the 

 anatomy of the animals, namely, the small size of the foot, the presence of well 

 developed labial palps, the single posterior siphonal orifice, and also the reo-ular 

 want of lateral teeth in the shells, their thin and silky internal structure, the form 

 of the muscular impressions, &c., we must regard the present family, in the manner 

 introduced by H. and A. Adams in their "Genera," as a small natural group of 

 shells. 



In their geological history the Ungulinid^ also differ somewhat from the 

 LuciNiB^. There are some forms known already in paleozoic (Silurian and 

 Carboniferous) rocks, very strongly resembling in external shape Vngulina, and 

 which have been described under that generic name ; but sufiiciently authenticated 

 species of the family are as yet only on record from cretaceous and younger 

 deposits, their number slightly increasing up to the present date. On the whole, 

 these shells are always rare. 



3s 



