32 i\ilj:umvlogy of ni:\\' york. 



genus. In an appendix to tlieir 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 aililiations 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 ])otli valves of the type-species, L. 

 U'hitfieldi, but also of two other species, L. Norwoodi and L. Granti. These 

 have furnished indisputable evidence of Trimerelloid characters, and show the 

 lirst deviation in this direction from the typical Lingula. Added to this is the 

 genus LiMiiLASMA, 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 Trimerellidae under the foregoing definition 

 of this group, nor can they be properly included under the Lingulidae, 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 Li.ngula. The lateral and 

 terminal impressions are undoubted analogues of those occupying similar posi- 

 tions ill L. anatina {i, /, /, in the pedicle-valve; /, /, k, in the brachial), and 

 tliough evidently compound, it has been hitherto irapo.s.sible to resolve them 

 into more than two distinct pairs of scars. The median impression, /. e., that 

 covering the surface of the platform, is readily resolvable into central, lateral. 



