BRACHIOPODA. 
119 
Comptes rendus,* but in 1849,f in giving a list of species referable to the genus, 
the first mentioned is Orbicula Buchi, Yerneuil, and it seems that 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. 4-5. 
1861. Helmersenia, Pander. Bull, de l’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 caecal (?) 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 Prodrome de Paleont. Stratigraphique, p. 20 
