BRACHIOPODA. 119 



Comptes rendus,* but in 1849,f in giving a list of species referable to the genus, 

 the first mentioned is Orbicula Buchi, Verneuil, and it seems tliat this must be 

 taken as the type of the genus Orbicella. Under the rigid enforcement of the 

 current rules for the recognition of priority of nomenclature, Keyserlingia 

 becomes a synonym for Orbicella, D'Orbigny, although this construction of 

 the matter does no justice to the intentions of the authors of either generic 

 term. 



Genus HELMERSENIA, Pander. 1861. 



PLATE IV, FIGS. 1-5. 



1S61. Helmersenia, Pander. Bull, ile I'Acad. Imp. des Sciences de St. Petersbourg, vol. iii, p. 47, pi. 



ii, tig. 2, a-g. 



Diagnosis. Shell having the general form of Obolus, with a prominent car- 

 dinal area depressed in the center by a broad, low pedicle-groove (?). Apex of 

 the ventral valve truncated by a circular hole, which is not produced into an 

 internal tube. Muscular impressions indistinct. No specific name has been 

 proposed for the typical form. 



Like the foregoing, this genus shows, in its csecal (?) apical tube and oboloid 

 cardinal area, characters allying it to both Siphonotreta and Obolus, and, like 

 Keyserlingia, also needs a verification of its peculiar features before its proper 

 relationship can be demonstrated. 



* Vol. XXV, p. 269. 



t Pi-odi'ome de Paleont. Stratigraphique, p. 20 



