BRACHIOPODA. 23 



valve. Furthermore, these considerations require us to regard the crescent in 

 LiNGULOPS as not homologous with tlie same feature in the Trimerellids, a con- 

 chision 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. 



