194 
PALEONTOLOGY OF NEW YORK. 
the Liorhynchus limitaris, Vanuxem, frequently constitute entire strata of some 
inches in thickness; and also, in the more bituminous layers of the Hamilton 
group proper, L. muUicostus, Hall, and at times, L. quadricostatus, Hall, become 
very abundant, and are correspondingly rare as the shales lose their organic 
matter and become more calcareous. In the black Genesee shales, L. quadri¬ 
costatus, Hall, is often abundant. Where the succession of the sediments was 
more persistently calcareous or arenaceous the shells adapted themselves to 
their surroundings, though under such circumstances not attaining so great 
development in individuals. In the calcareous layers of the Hamilton group 
at Thedford, Ontario, L. Laura, Billings,'*' is not of infrequent occurrence. L. 
Kelloggi, Hall, occurs in the upper Devonian calcareous sandstones of northern 
Ohio; L. mesacosialis, L. sinuatus. Hall, and L. globuliformis, Vanuxem,f in the 
sandstones of the Chemung group; the L. Newberryi, Hall and Whitfield, from 
the Erie shales, of Devonian age ; the L. Greenianus, Ulrich, from the Knobstone 
formatiou of Keokuk age, and the L. Boonensis, Shuniard, in the Burlington 
limestone. 
In the later representatives of this subgenus there is a tendency to obsoles¬ 
cence of the plications over the entire surface; and in all specimens where the 
interior is well preserved, the muscular impressions of the brachial valve form 
narrow, elongate-oval scars alongside the median septum. Frequently, also, 
the narrow pit beneath the hinge-plate supported by the median septum, is 
of conspicuous size, as in L. globuliformis. The significance of the group of 
fossils embraced by the foregoing divisions, Camakot(BCHIA, Plethorhynchus 
and Liorhynchus cannot be gainsaid. The existence of an incipient spondyl- 
ium between the divisions of the hinge-plate, supported by the median septum, 
at once indicates a relationship, not so much to the pentameroids, which have 
for the most part preceded these in time, but to the spondylium-bearing shells 
of the later palmozoic periods, Camarophoria and its allies. 
* Some of the more oblate forme of this species seem indistinguishable from L. multicoslus. Hall, but 
L. Laura normally has an elongate-oval outline which is not possessed by typical examples of the former. 
t Before us is a specimen of the Rhynclionella caslanea. Meek, fi-om the Eureka District of Nevada, 
agreeing with Mr Walcott’s identification of this species as described in volume viii. Monographs of the 
U. S. Geological Survey, p. 153. This specimen demonstrates a very close specific similarity to Liorhynchus 
globuliformis, Vanuxem, and serves to fix its generic relations beyond doubt. 
