RHYNCHONELLID. 197 
Abroad M. de Verneuil states it to be one of the most characteristic fossils of the 
Lower Silurian rocks of the north of Russia; that the variety rofunda occurs in Norway, 
from whence it has been quoted by M. d’Hichwald; and that Mr. Bunbury brought the 
shell from the neighbourhood of Christiania, in whose collection M. de Vernewl saw a 
specimen. P. intercedens and its varieties are abundant at Pavlosk, Popova, Poulkova, 
Reval, &c., in Russia. 
Genus—Tripiesia,’ Hall, 1859. 
The characters belonging to this genus have not been as yet completely made out. 
Prof. Hall describes it as follows : 
“ Shells transverse or elongate, trilobed or subtrilobate, ventral valve being marked by 
a broad deep sinuosity, and the dorsal valve by a corresponding fold. Hinge-line straight; 
area small, foramen triangular. External surface concentrically striated, and with fine, 
obscure or obsolete, radiating striz ; internal structure not determined. 'Types—Aérypa 
extans, A. cuspidata, and A. nucleata.” 
In a paper “On some Rocks and Fossils occurring near Phillipsburgh,” published in 
August, 1861, Mr. Billings considers Zriplesia, Vall, to be a synonym of his own genus 
Camerella, described in the ‘ Canadian Naturalist and Geologist,’ vol. iv, p. 301, August, 
1859; but I doubt much, as does Prof. Hall, that the two can be synonymous, and 
certainly C. longirostra and C. varians, Billings, do not belong to the same group or 
genus as Z)iplesia extans, or to the species Iam about to describe. Moreover, Mr. Billings 
observes, at p. 8 of the paper above named, that ‘The genus Camerella appears to belong 
to the family Rhynchonellide, the species differing from the ordinary forms of Rhynchonella 
by having the surface in general either not ribbed at all, or with only a few obscure 
plications, not extending to the beak. The interior differs in having the dental plates of 
the ventral valve converging so as to form a small triangular or oval.chamber of variable 
dimensions, as in Pentamerus.” 1 have considered it necessary to refer to these details 
to show that Zrzplesia, Hall, cannot be the same as Camerella, for in Triplesia we have 
a straight hinge-line, area, deltidium, and foramen at its extremity, none of which characters 
belong to Camerel/a. Unfortunately, the internal arrangements of Tiriplesia do not 
appear to have been hitherto discovered ; and I have no material which would enable me 
to throw light upon the subject. The genus must, consequently, be provisionally received ; 
and it would be very desirable that good internal casts of 7. extans and 7. Grayie should 
1<Twelfth Report on State Cabinet of New York,’ p. 44, 1859. Gr. rperAastos, triplex, in reference 
to the trilobed character of several of the species. 
