BRACHIOPODA. 
15 
Proderi of the Hudson group, L. cuneata of the Medina sandstone, L. centri- 
lineata of the Lower Helderberg, L. pundata, 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 with 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 difference 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, but 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 rarely given any 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 sul>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. Surv. United Kingdom, vol. ii, pt. 1, p. 370. 
t For description, see Supplement. 
