MOLLUSCA. 
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rounded, the umbones more central ; it has more the shape of Baudon’s pi. Ill, fig. D, than 
the last species has. 
Diam. 2J, alt. 2, crass. If mm. 
About a dozen specimens from Yarkand. 
30. PlSIDITTM, n. sp. 
This small form is quite distinct from the two preceding ; it can he at once distinguished 
by its great flatness, by being more broadly truncate anteriorly, more produced posteriorly, 
by its very flatly appressed umbones and by its polished glabrous surface ; it resembles Bau- 
don’s pi. ii., fig. E, (P. thermale, Dup.), and also somewhat “ Eedsch. Moll.,” pi. iii., fig. 33, 
though apparently the latter does not possess the characteristic appressed umbones. 
Diam. 3, alt. 2f, crass I- 3 - mm. 
Only two or three specimens from Yarkand. 
31. PlSIDIUM OBTUSALE, Pfl\ 
Agrees fairly with Clessin’s figure of P. obtusale, loc. cit., pi. ii., fig. 22. 
Diam. 4f, alt. 3f, crass. 2f mm. 
About twenty specimens from Pankong Lake. 
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