BRA CHIOP ODA . 
23 
valve. Furthermore, these considerations require us to regard the crescent in 
Lingulops as not homologous with the same feature in the Trimerellids, a con¬ 
clusion which seems unwarranted and apriori improbable. This point is, how¬ 
ever, maintained by the authors, who, regarding the valve as brachial, suggest 
that the crescent “ was produced by the attachment of the outer muscular cord 
and associated vessels” of the setal band (p. 166), a statement in direct con¬ 
travention of that on page 165, viz., “the second” (the “arched fillet” or 
crescent) “ is evidently the equivalent of the crescent characterizing the 
Trimerellids”; and these authors were the first to demonstrate that this 
crescent is, essentially, a parietal scar. 
The interior of the brachial valve in Lingulops Whitfieldi shows the cardinal area 
and pedicle-groove (as already noticed), and the crescentic ridges essentially as on 
the opposite valve. The muscular scallops are represented by three depressions, 
closer together than in the other valve. The most striking and important 
feature, however, is the platform, sharply developed and showing on its surface 
faint indications of the median and lateral muscular scars. This organ is even 
more strongly developed in L. Norwoodi and L. Granti, but in none of the species 
is it continued into a longitudinal septum. The vascular sinuses have been 
observed in L. Whitfieldi only, and these appear to be closely similar to those of 
Lingula. 
With its several linguloid characters well defined, Lingulops presents both 
in its platform and crescent, evidence of a close alliance with the Trimerellids. 
It is in this genus that appears the first satisfactory evidence of the develop¬ 
ment of the platform. That this tendency should have advanced farther in 
the brachial than in the pedicle-valve, is quite in accordance with the relative 
degree of development seen in opposite valves of the same species in Monomer- 
ella and Dinobolus. The elevation of the anterior portion of the muscular scars 
in the pedicle-valve in the earlier species, L. Whitfieldi and L. Norwoodi , must 
be regarded as the inception of this tendency toward the elevation of the entire 
area of muscular insertion, which we find effected in the latest known repre¬ 
sentative, L. Granti. 
