172 Records of the Indian Musl-udl [Vol. XIX^ 



In a previous paper ' I referred to the soft-parts of this form 

 and included a description and drawing of its glochidium. A few 

 further notes are here included. The inner pair of gills are much 

 broader than the outer, and the outer pair of gills alone is marsupial. 

 The palpi are elongate but rather shorter than in L. marginalis. 

 The foot and the adductor and retractor muscles are very well 

 developed. The branchial is double the size of the anal, 

 which is of about the same size as the supra-anal. The animal on 

 the whole has a much heavier build than that of L. marginalis 

 and differs from it fundamentally in the outer pair of gills alone 

 being marsupial. 



The species though closely allied to L. marginalis differs from it 

 in the heavier build of the shell, in the umbones being larger, more 

 prominent and swollen, and in the hinge being more highly 

 developed. 



Hanley and Theobald's specimens of this form were obtained 

 from the Irrawad}^ river in Burma, but the species has a much 

 wider range in Burma, Assam and Eastern Bengal. In the Indian 

 ^Museum collection it is represented by specimens from Tong- 

 hoo, Burma; Silchar, Cachar and Sylhet, Assam; and from Chit- 

 tagong and Dacca, Eastern Bengal. 



Lamellidens jenkinsianus (Benson). 

 (PI. IX, figs. 3, 4.) 



1862. Unio jenkinsianus, Benson, A7in. Mag. Nat. Hist. X, p. 185. 

 1876. Unio jenkinsianus, Hanley and Theobald, op. cii. p. ig, pi. xli, 



fig. 4. 

 1900. Lamellidens /oikmsianus, Simpson, Proc. U. S. Nat. Mits. XXII, 



1914. Lamelhdens jenkinsianiis, Simpson, Descr. Cat. Natades, pp. 1176, 



1915, Lamelh.dens ?nargi72alis, subsp. jenkinsianus, Preslon, op. cit. p. 184. 



Benson's and Simpson's descriptions are fairh' complete so far 

 as the form of the shell is concerned, but as the peculiarities of 

 the hinge have not been noticed by either author the}' are described 

 here. Right valve with two pseudocardinals, of which the lower is 

 rather long, extending from close abov^e the scar of the anterior 

 adductor muscle to the middle of the beak ; it is very thick and 

 heavily built, sometimes a little curved and very ragged ; the upper 

 one is usually thin and does not extend so far. There is a single 

 blade-like lateral, rather shorter in the typical form but thicker 

 and a little more arched. Left valve with a single pseudocardinal and 

 a small pad-like tooth arising from the inner margin of the beak, 

 and two lamellar teeth of the same type as in the typical form 

 but thicker. 



This form differs from the subsp. obesa in being less in- 

 flated and less deep but more solid and relatively more elongate, 

 in the muscle-scars being more impressed and the hinge much 

 more strongly developed. 



' Rec. hid. Mas. XV, p. 145, fig. la (1918). 



