CLASSIFICATION OF THE BRACHIOPODA. . 133 



Geol. range. — The genus has not hitherto been discovered above the Silurian 

 deposits. 



Examples : S. unguiculata, Eichw., sp. ; verrucosa, Vern. ; fornicata, Kut. ; comoides, 

 Kut. ; A?iglica,M.on\s,; micula, M'Coy. 



Section A. Sub-Genus — PAcrotreta, Kutorga, 1848/ 

 Tijpe — A. SUBCONICA, Kut. Int., PI. IX, figs. 2/1 — 275. 



Animal unknown ; shell triangular, larger valve conical ; false area flat, and bent back 

 at right angles to the margin of the valve, longitudinally grooved along the centre, and 

 perforated at its extremity by a small circular aperture, the lines of growth encircle the 

 shell and pass uninterruptedly over the false area ; the smaller valve is almost flat and 

 opercuUform, smooth, and marked by concentric lines of growth. Valves unarticulated ? 



Obs. Never having been able to procure the inspection of any examples of the species 

 composing this genus, I can offer no decided opinion on the subject. Professor Kutorga 

 places this section m his family Siphonotretaeae ; Mr. Morris, on the contrary, seems 

 disposed to consider Acrotreta identical with Cyrtia^ in which opinion I cannot 

 coincide, if the figures drawn by the distinguished Russian Palaeontologist be correct, and 

 of which I feel little doubt. The shape of the false area, the hollow groove, and the 

 perforation of the summit of the truncated beak, are characters not observable in any 

 species of Cyrtia? 



Geol. range. — Not hitherto observed above the lower Silurian beds of Russia. 



Examples : A. subconica, disparirugata, and recurva, Kut. 



Family— LINGULIDtE. 



Animal fixed by a muscular peduncle passing out between the beaks of the valves ; 

 arms fleshy, unsupported by calcified processes. Shell unarticulated and sub-equivalve ; 

 texture horny. 



Obs. The family is composed of two genera, Lingula and Obolus. 



^ Uber die Siphonotretaeae aus den Verhandlungen der Kaiserlichen Mineralogischen Gesellschaft fiir 

 Jahr 184", tab. vii, figs. 7 — 9. 



2 Ann. and Mag. of Nat. Hist., vol. iv, No. 23, p. 315, 1849. 



^ Having communicated on the subject with my friend Dr. Volbortli, of St. Petersburgh, that gentle- 

 man states — " Sur aucun de mes e.xemplaires d^^ Acrotreta je n'ai pu constater de charnifere ni d'apophyses 

 dentaire ; mais le nombre des echantillons est si petit que je n'oserai emettre une opinion positive a se 

 sujet ; cependant la physionomie gen^rale de cette espece la i-approche tellement des Siphonotretaeae que je 

 leur assignerai des valves libres tant que je n'aurai les charuieres et les dents devant moi." 



