32 
PALAEONTOLOGY OF NEW YORK. 
genus. In an appendix to their paper, the authors mentioned discussed the 
character of the genus Lingulops, then known only from the interior of a 
single valve, and pointed out its affiliations with the Trimerellids. Of this 
genus also our knowledge has greatly progressed, and we have now not only an 
accurate understanding of the interiors of both valves of the type-species, L. 
Whitjieldi, but also of two other species, L. Norwoodi and L. Granti. These 
have furnished indisputable evidence of Trimerelloid characters, and show the 
first deviation in this direction from the typical Lingula. Added to this is the 
genus Lingulasma, recently described by Mr. E. 0. Ulrich, which presents 
another interesting and important link in the development of this family. 
These latter genera (and we have elsewhere adverted to the same subject 
more at length) are neither true Trimerellidse under the foregoing definition 
of this group, nor can they be properly included under the Lingulidse, except 
as a matter of convenience in classification, and we here meet, as we often 
do in the study of the inarticulate brachiopods, an emphatic protest against 
the unnatural rigidity of any scheme of classification, requiring the alignment 
upon the same plane, of forms which may be, in various directions, successive 
and gradational. 
The anatomical features of these shells calling for especial attention are (1) 
the platform, (2) the umbonal chambers, (3) the muscular scars. The first two 
are treated in reference to their development and functions in another place 
(see page 46). ' The last is most remarkable for the striking specialization 
of the so-called “ crescent,” a sub-marginal, cardinal impression, skirting the 
posterior area of the shell in both valves and terminating in, or just enclosing 
at about the middle of the sides, a prominent, sometimes compound scar. This 
is believed to be the impression of a strong muscular post-parietal wall, its 
position being quite analogous to the same feature in Lingula. The lateral and 
terminal impressions are undoubted analogues of those occupying similar posi¬ 
tions in L. anatina (i, j, l, in the pedicle-valve; l, i, k, in the brachial), and 
though evidently compound, it has been hitherto impossible to resolve them 
into more than two distinct pairs of scars. The median impression, i. e., that 
covering the surface of the platform, is readily resolvable into central, lateral, 
