REVIEWS—CONTRIBUTIONS TO PALHONTOLOGY. 189 
erebescens, certain examples of which have been found to exhibit a well- 
marked area. The genus Skenidium, founded on orthis insignis, is char- 
acterized by the prolongation of the cardinal process into a median sep- 
tum which extends to the base or front margin of the shell, and occasion- 
ally bifurcates at this lower extremity. In the typical species, the area 
is large and triangular, but this character, although cited by the author 
in the generic description, is probably more or less inconstant. It 
would, at least, be manifestly unsafe to refer to this genus (allowing it 
to be really distinct) all the orthis-like forms with large area, high ven- 
tral valve, and radiating striae, where other characters could not be 
observed ; and yet, in nine cases out of ten, these external characters are 
alone open to us. The genus <dAmbocelia, of which the long-known 
orthis umbonata of Conrad is the type, possesses a large and curved 
beak in the highly convex ventral valve, and a four-parted muscular 
impression near the centre of the dorsal valve. The proposed genus 
Vitulina somewhat resembles the author’s Tropidoleptus, but the 
dental processes are not crenulate, nor distinctly separated from the 
area, as in the latter. One species only is cited: V. pustulosa from 
the Hamilton Group of Genesee County, New York. The genus 
Meristella is separated from Merista (with which the author’s Cama- 
rium is now seen to be identical) by the absence of the peculiar 
arched, or “shoe-lifter,’’ process, belonging to the ventral valve of 
that genus. From Athyris, on the other hand, it is distinguished 
chiefly by the presence of a well-marked median septum, absent, or 
rudimentary, in the former, and by a slightly different muscular im- 
pression ; but these characters are surely insufficient to warrant the 
Separation, even if they should prove to be constant. Finally, Levo- 
rhynchus is made to include the meristella or athyris-like forms with 
plications on the central portion (or, occasionally, on the entire sur- 
face) of the shell. Internal spires have not yet been recognised, so 
that the family to which this type should be referred, cannot be 
strictly determined; and great difficulty must be experienced, if the 
genus be adopted, in distinguishing many of its species from those of 
athyris or rhynconella. 
In the Devonian rocks of Western Canada, the genus Lingula 
appears to be of exceedingly rare occurrence, but, from strata of this 
age in New York, Professor Hall has described several species of com- 
paratively large size, together with a large species of Discina, and 
several species of Crania. Some forms referred to the genus Tere- 
