BRACHIOPODA. 15 



Proderi of the Hudson group, L. cuneata of the Medina sandstone, L. centri- 

 lineata of the Lower Helderberg, L. punctata, L. Delia and L. densa of the 

 Hamilton, etc. While in many cases it has not been observed and in other 

 species is known not to exist, it must be borne in mind that all specimens of L. 

 anatina do not show the internal ridges witli equal distinctness, and that not 

 infrequently they are all obsolescent. It will therefore be a matter of much 

 difficulty, if it be possible, to fix upon features of permanent taxonomic value 

 in the development of these septal ridges. 



In DiGNOMiA (L. alveata) it is an important fact that both median and lateral 

 ridges appear to be nearly equally developed in both valves, and herein 

 lies a distinctive diiference between this form of development and that charac- 

 terizing either Lingula anatina or Glottidia. It would not be prudent to attempt 

 a further sub-division of Lingula on septal features alone, although one cannot 

 but recognize the great differences of development in these respects. Dignomia, 

 however, may be tentatively accorded a sub-generic value until its further rela- 

 tion to, or divergence from Lingula can be demonstrated. 



In 1848, Phillips proposed to place such forms of Lingula as L. attenuata, 

 Sowerby, and L. crumena, Phillips, in a separate group under the designation 

 Glossina.* The author seems not to have given a diagnosis of the characters 

 of the division, l^ut evidently intended to include in it a pretty well defined 

 group of forms. Our knowledge of the internal characters of these earlier 

 acuminate forms is very imperfect, as they have rarel}- given anv indication of 

 muscular impressions or septal markings, and it may eventually be advisable 

 to separate this group from typical Lingulas, under the name proposed by Phil- 

 lips. We must not overlook the fact that L. cuneata has shown muscular scars 

 having the general character of those in L. anatina, but this species deviates slightly 

 in the sub-quadrate tendency of its outline from the group of sub-trigonal forms 

 constituting Glossina. Mr. Davidson has also shown that similar scars exist in 

 L. Hawkii, Rouault, a species having the broadly spatulate character seen in 

 L. flabellulaf and L. Scotica. 



* Mem. Geol. Sui-v. United Kingdom, vol ii, pt. 1, p. 370. 

 t For description, see Supplement. 



