BRACHIOPODA. 
89 
In the brachial valve, the posterior portion of the margin is considerably 
more flattened and that portion of the outline of the valve quite transverse. 
Directly within this margin, and parallel to it, is a narrow thickened band, 
which may be analogous to the callosity occupying a similar position in 
Waagen’s genus Neobolus. There is also a muscular thickening or callosity 
of about the same size and character as that seen in the pedicle-valve, but 
somewhat more flabellate, less distinctly defined, and not satisfactorily resolvable 
into separate scars. A faint median septum begins near the posterior margin 
of this area and grows in size until the anterior end is reached, whence it 
rapidly disappears. No evidence has been found of curved laterals similar to 
those in the pedicle-valve. Mr. Ulrich’s figures show in both valves peculiar 
circular sears situated near the lateral margins. These are mentioned in the 
diagnosis as being “ very faint ” and indeed are visible only on the best pre¬ 
served specimens, and there only under the most favorable illumination. If it 
can be demonstrated that these markings actually represent muscular scars and 
are not the result of a slight exfoliation, they will prove a feature of much im¬ 
portance. None of the forms of Obolella, or allied genera known in primordial 
or Silurian faunas, show a combination of the elongate curved lateral scars with 
such additional impressions, and we find an analogous occurrence only in the 
genus Lakhmina, (Ehlert, from the Salt Range of India,* a genus with a well- 
developed platform, remarkable not only as being the earliest representative of 
the Trimerellids, but also for its synthetic characters, for in association with 
the “ laterals,” or outside marginal scars, which undoubtedly represent the 
terminal impressions of the crescent, are the peculiar curved laterals of 
Obolella. Better material must be examined in order to determine the ex¬ 
istence or non-existence of these crescent scars in Schizobolus. This genus, 
with our present knowledge, appears to be a very late representative of the 
true obolelloid type, as pointed out by Mr. Ulrich, varying therefrom more 
in the character of its pedicle-slit and cardinal area than in any other 
feature, but in its triangular pedicle-opening indicating a relationship to 
Trematis and Schizocrania. 
* See Waagen, Mein. Geol. Survey of India, Salt Range Fossils, vol. i, pt. iv, fasc. 5, p. 764, pi. lxxxv, 
fig. 6, 1885; Davidsonella linguloides. 
