19.18.] Ekendranath Ghosh: Anatomy of TJnionidae, 115 



wards from below, and in Physunio only marked in the right side. Be- 

 hind the conical elevation is another slight eminence which receives the 

 opening of the intestine in Solenaia. In LameUidens the opening lies on 

 or behind the eminence, while in Physunio it is placed behind it at the 

 bottom of a cup-shaped depression itself surrounded by a raised margin. 

 In all cases the opening of the intestine is placed to the left side of the 

 middle line. 



The posterior wall of the stomach is raised into a transverse fold iu 

 the middle of its width giving rise to two blind pouches ; the fold is 

 continued into the lateral wall of the stomach, more in the case of Lamel- 

 lidens than in the two other genera. The dorsal pouch is directed 

 upwards and backwards, while the ventral pouch is directed transversely 

 backwards. 



In Solenaia there is another fold in the backwall of the dorsal pouch 

 above the transverse one which passes obliquely outwards and down- 

 wards to meet the transverse fold at the side ; this ridge is faintly marked 

 or absent in LameUidens, but in Physunio ferrugineus a similar ridge, 

 arising from the dorso-lateral corner of the dorsal sac, passes downwards 

 and forwards to meet the transverse ridge at the postero-lateral wall 

 of the stomach ; it is present only on the left side but a faint trace of it 

 can also be made out on the right side. In this species also a fold arises 

 from the right side of the cup-like depression (in which the opening of the 

 intestine is placed), which passes obliquely upwards and to the right on 

 the posterior wall of the stomach and ends below the transverse fold 

 in the postero-lateral corner ; two other smaller and less prominent 

 ridges are seen, one arising from the postero-lateral aspect of the margin 

 of the same cup-like depression to the right and the other a little above 

 the preceding from the oblique ridge, both passing to the left. Another 

 strongly marked ridge is also found in the right lateral w^all of the sto- 

 mach at the level of the margin of the cup-shaped depression, continued 

 behind to the origin of the oblique ridge from the margin of the cup. 

 It forms a deep pouch on the ventro-lateral aspect of the stomach, the 

 lower boundary of which is formed by the raised lateral margin of the 

 cup-shaped depression. 



In all the three genera the transverse ridge from the posterior wall 

 of the stomach, as it passes to the left side, fuses with one from the antero- 

 dorsal wall above and with another from the ventral wall of the stomach 

 at its junction with the oesophagus, with the formation of a separate 

 portion of the dorsal pouch on the left side. 



(d) Intestine. — The coils of the intestine in the visceral mass are 

 similar in fundamental arrangement in all the genera considered here. 

 They may be best described in a tabular form : — 



Loop of the Intestine. L. marginalis. Solenaia soleniformis. Physunio. 



(1) First loop, from Course backward Much more bacli- Much more down- 

 the stomach to and downward. ward than down- ward than back- 



tlie posterior end ward. ward, 



of the visceral 

 mass (course 

 backward and 

 downward on 

 the left side of 

 the middle line). 



