156 
PALAEONTOLOGY OF NEW YORK. 
appear to be sometimes complicated by association with ill-defined scars of the 
anterior muscles. The posterior adductors or divaricators are situated at the 
basal angles of the muscular triangle, and are distant from the posterior mar¬ 
gin. The linear parietal scars are very strong, the posterior being more or less 
distinctly lobate, the anterior generally straight or rounding about the central 
adductors. In the opposite or dorsal (?) valve the scars have essentially the same 
arrangement; the anterior adductors,however,are separated by elongate median 
scars (anteriors) which traverse the elevated callosity surrounding the anterior 
margin of the area. The posterior scars are often more widely divergent than 
in the other valve. Shell-substance calcareous and impunctate (?). 
Type, Pholidops squamiformis, Hall. 
Observations. This peculiar group of shells presents an interesting associa¬ 
tion of features which, so far as known, is susceptible to slight variation. The 
character of their muscular anatomy is distinctly cranioid, as seen in the 
development of the two strong pairs of adductor scars, but the concentration 
of the muscular impressions and the resulting removal of the posterior scars 
forward from the margin is a feature not seen in any Crania ; added to this 
is the usually sharp impression of the parietal wall which is rarely observable 
in any of the inarticulates except the Trimerelloids. The posterior lobate 
limb of this impression in Pholidops is suggestive of the scalloped or sinused 
arch seen in Lingulops* but we should hesitate to suggest an analogy between 
the two. 
The depth of the muscular impressions in Pholidops, evidently an index of 
the strength of the muscular bands, is a natural result of their concentration 
within the confined visceral area, for by such a displacement a great advantage 
in the closing of the valves is sacrificed. 
In external features, outline and contour, there occur some noticeable varia¬ 
tions. The typical species, P. squamiformis , with oval outline and subcentral 
beak, represents the character of exterior prevailing among the species 
* In discussing- the genus Lingolops, we have indicated that the scar of the parietal wall constitutes 
the crown of the crescent and that there is no satisfactory reason for ascribing to the cx-escent in Lingulops 
one function, and to that in Trimkrella anothei*, as was done by Davidson and King. 
