ORTHID A. 231 
opposite one, with a slightly prominent fold or rounded elevation corresponding with the 
sinus in the opposite valve; beak small, area narrow, fissure triangular. Surface orna- 
mented as in the dorsal valve, while both valves are likewise crossed by strong concentric 
lines of growth. Three specimens measured— 
Length 2, width 3 lines (usual size). 
mn, Loa tes 
ile OS ah stn Oise 
Oés. Although this shell occurs by millions in certain rocks, it is exceeding rare to 
meet with a tolerably complete example. The shellis found under the conditions of casts 
and impressions which are so much distorted from the effects of pressure that it is often 
impossible to make out the real shape and character. Mr. Salter observes that it is a 
very well-marked and pretty species, that the length is less than the breadth in the 
proportion of seven to nine; the number of ribs varying greatly, but not in a manner 
to make him believe we have more than one species. Although usually small, some 
examples appear to have attained nearly half an inch in length and breadth; for after 
a close examination of some hundred examples of all sizes, varying from two to 
nearly six lines in length, I could perceive no other differences than that in some 
examples the ribs were a little more numerous and closer than in others, and that the 
very large examples have been to some extent extended by pressure. There can, there- 
fore, exist no doubt as to the value of this little species, so characteristic of the Upper 
Lingula-flags of both North and South Wales; but the application of the name here 
given is still attended by some uncertainty. 
In 1821 Wahlenberg described, but did not figure, his Anomites lenticularis in the 
following words :—“Suborbicularis utrinque convexiusculus radiatim undulatus. In 
; compressed, unusually large example. 
lapide suillo strati schisti aluminaris per plures provincias passim copiose sedet, in quo 
lapide nulla alia testacea unquam lecta sunt. Magnitudine et situ Entomostraciten pisi- 
formem in eodem lapide provenientem aliquanto refert. Utraque valvula pari convexitate 
gaudet, adeo ut conjuncte semina lentis proxime equent. Valvulz substantia sua 
tenuissime fuisse videntur.” Subsequently both Dalman and Hisinger redescribed 
Wahlenberg’s species, without figuring it, under the designation of Atrypa ? lenticularis. 
Von Buch makes of it a Spirifer, and Salter an Orthis. In 1865 Kjerulf* both describes 
and figures what he takes to be the Atrypa ? lenticularis of Dalman, adding Orthis vati- 
cina, Salter as a synonym, and Atrypa micula, Dal., as a closely allied species. In his 
description of O. /enticularis Mr. Salter observes that he does not see in the Scandinavian 
specimens from Kinnekulle, in West Gothland, sufficient differences to warrant him in 
separating it from the British examples, and that he has but little doubt that the shell 
under description is Dalman’s species from Egeberg, though the specimens in the Survey 
Collection have less prominent ribs, and a generally smoother appearance; but that 
1 « Vejviser ved geologiske excursioner 1 Christiania Omegn.,” 1865. 
