46 G. F. MATTHEW ON THE 



OETHIS, Dalman. 

 Orthis lenticulakis. "Wahl. (PL XII, figs. 9 a-d.) 



\?,2\—Anomile8 leniknlarig. Wahl. ' Petr. Tell. Suec' p. 66. 



19,21— Alrypaf lenticularh. Daim. ' Vet. Acad. Handl.,' p. 1.32 ; ' His. Leth. Suec.,' p. 76. 



\iZ\—Spi-riferf Imticularh.. L. von Buch. ' Abhandl. d. Berl. Acad.,' p. 18. ïab. i, figs. 13-14. 



jg^^ I Atrypa lenticularis. Kjerulf. ' Geol. d. Sûdl. Norw.,' p. 284 ; • Veiviser,' etc., p. 1-3, fig. 7. 



18m— Orthis hnticularis. Dav. ' Geol. Magaz.,' vol. v. Tab. xvi, figs. 20-22. 



JS71— Orthis lenticularis. Dav. ' Brit. Silur. Brach.,' p. 230. Tab. xsxiii, figs. 22-28. 



The following is Wahlenberg's original description of this species : 



" Suborbicnlar, on each side a little convex, radially undulate. In a ' suillous ' rock 

 (foetid limestone) in beds of aluminiferous slate, in which material no other shell has been 

 found. It occurs plentifully everywhere throughout several provinces. In size and iu 

 its situation it resembles at first sight the pea-shaped entomostracan [Agnostiis pisiformis, 

 which occurs] iu the same rock. Each valve rejoices in an equal convexity, so that when 

 united they very much resemble the seed of a lentile. The valves are seen to have been 

 very thin in their substance." ' 



Caiman's description is fuller, and is as follows : " A small species, with very tender 

 and fragile valves. Length about 4 mm., and of about the same, or somewhat greater 

 breadth. An entire specimen is rarely found, but the species is most easily distinguished 

 on account of the stone in which it occurs, as it has scarcely any other species of Terebra- 

 tulite with it. The shell is suborbicular, with the base somewhat prominent and a little 

 convex ; toward the margin it is sensibly compressed. Strife of undulating lines, lines in 

 number abou.t twenty, but indefinite. "Without a yoke [deltidiumj or canal to the dorsal 

 [ventral valve ?]. In the complete state no transverse furrows have been observed, but 

 deprived of the epidermis [outer shelly layer], the radiating striœ are wanting, and the 

 shell appears concentrically striulate. The true structure of the hinge is not rightly 

 explored, but, on account of the external aspect and its place in the most ancient strata, 

 the species is suspected to belong to the genus Alrypa." - 



Leopold von Buch, iu the work above cited, presents us with another view of this 

 species, and from his impressions of its form and relations referred it doubtfully to the 

 genus Spirifer. His account is as follows : 



' Wahlenberg, Petr. tell., p. 60 —^nomito feniicWaris— Suborbicularis utrinque convexiusculus, radiatira undu- 

 latus. In lapide suillo strati scliisti almninaris per plures provincias passim copiose sedet, in quo lapide nulla alia 

 testacea unquam tecta sunt. JIagnitudine et situ entomostraciten pisiformem in eodem lapide provenientem ali- 

 quanto refert. Utraque valvula pari convexitate gaudet, adeo ut conjunctse semina lentis proxime aequent. 

 Valulse substantia sua tenuissimse fuisse videntur. 



2 Species parva, valvis tenerrimis et fragilibns. Longit. circiter 4 mm., et ejusdem latitudinis vel ultra. 

 Specimina intégra raro inveniuntur. Species vero lapide in quo .sedet facillime distinguenda, quum vix aliam 

 tertbratulitarum speciem babeat sociam. 



Testa suborbicularis basi aliquantum prominula et convexiufcnla, versus wargines sensim compressa, 

 striœ radiantes lœves, underum vistie (numéro circiter 20, 1. indefinite). Absque jugo, canali dorsali, statu integro 

 nullte observantur, strije transversales, sed epidermidfp detrita strite radiantes deficiunt, et testa apparent con- 

 centrice striolata. 



Cardinis vera structura baud rite explorata sed ob faciem externum, et locum in stratis antiquissimis species 

 esse Atrypee generi suspicatus sum. 



