1876.] 45 [Call. 



cosia and Ligea (which are respectively simply the smooth and sculp- 

 tured forms of Baikalia) the names Liobaicalia and Trachybaicalia, 

 respectively. His names are exactly synonymous with those of 

 Dybowski, and no types being mentioned it is open to others to re- 

 strict the groups as their characters may seem to require. 



The largest, first figured and first described species of Benedictia is 

 B.frayilis Dyb. (1. c. p. 5, pi. i, f. 1-5), which may therefore stand 

 as the type. 



One or the other of the two names applied by Martens must be 

 strictly synonymous with Baikalia as the typical subgenus. Naturally 

 the most extensive of the two would be the one to be suppressed. 



The subgenus Trachybaikalia chiefly differs from Liobaikalia by 

 being ribbed, carinated or both. The genus Baikalia is in some of 

 its members related to or more probably identical with Tryonia of 

 Stimpson, from the typical species of which B. contabulata is hardly 

 more than specifically distinguishable. ProsostJienia Neumayr, is 

 also very closely related, and but for its thickened lip might be con- 

 sidered identical with Tryonia. The singular resemblance of Baikalia 

 Stiedce to Camptoceras Benson, can hardly be more than analogical. 



Two species of Baikalia present a feature which entitles them to 

 sectional rank, namely B. ciliata and Duthiersii ; whose ciliated epider- 

 mis strongly contrasts with the smoothness of the species associated 

 with them by Dybowski. With this character are associated a more 

 compact form and deeper sutures than most of the others exhibit. 



The division of the genus by sculpture is hardly warrantable. The 

 two groups fade insensibly into one another when tried by this test. 



Similar transitions are noticeable among the original forms of 

 Tryonia, which, like Baikalia, occupied an extensive inland lake, on 

 the ancient beaches of which they are now found in immense num- 

 bers. With these are to be compared the numerous forms described 

 from the Tertiaries of Central Europe by Brusina and Neumayr, 

 before the generic place of the group can be definitely fixed. 



The first species of Trachybaikalia (Ligea) mentioned by Dybowski, 

 is T. carinata, (1. c. p. 45, pi. iv, f. 1-4). The adult shell is figured, 

 contrary to the diagnosis, with a well marked anterior notch or 

 canal. But for this I should consider it fully synonymous with 

 Tryonia. The figure is possibly erroneous, but being without the 

 means of determining this for the present it may be considered as the 

 type of a distinct section. Otherwise, except in the case of Liobai- 



