CLASSIFICATION OP THE BRACHIOPODA. 135 



Sow. ; truncata, Sow. ; quadrata, Eichw. ; squamiformis, Phil. ; spatulata, Hall ; Credneri, 

 Geinitz ; tenuigranulata, M'Coy ; Davisii} M'Coy, &c. 



Genm — Obolus, Eichwald, 1829.^ 



Type—0. Apollinis, Eichwald. Int., PI. IX, figs. 280—285. 



Obolus, Eichwald, De Ferneuil, IfOrhiyny, and the generality of Authors. 

 Ungula, Fander? 

 Ojithis, V. Buch (part). 

 AuLONOTEETA, Kutorga.* 



Animal unknown. Shell sub-equivalve, orbicular, equilateral, slightly transverse or 

 elongated, depressed ; valves unarticulated, being held together by muscular action. 

 The larger valve (ventral of Owen) is most convex, with a short obtuse or pointed beak, 

 and wide flattened cardinal edge or false area, over which the semicircular concentric 

 lines of growth of the surface pass uninterruptedly ; the flattened cardinal edge is longi- 

 tudinally grooved by a semicylindrical furrow, destined to afford room for the passage of 

 the muscular fibres of attachment ; smaller valve rather shorter than the other, slightly 

 convex or almost flat, without any prominent beak or vertex, the hinge line forming a 

 regular arch, and passing imperceptibly into the lateral margins ; the cardinal edge is 

 likewise flattened and horizontally striated, but not interrupted by a mesial furrow ; 

 external surface smooth or irregularly sculptured by minute undulating wrinkles. 

 Structure calcareo-corneous. In the interior of the larger valve, a narrow slightly elevated 

 longitudinal ridge extends to about half the length of the valve, and four small oval 

 muscular impressions are situated one on each side near the cardinal angles, and 

 the other two towards the centre of the valve, a little beyond the base of the mesial 

 ridge. 



Obs. The genus Obolus was created by Professor Eichwald for the reception of two 

 Russian shells, which could not be properly admitted into any of the sections hitherto 

 established. MM. de Verneuil, Pander, D'Orbigny, Morris, &c., have most properly 

 considered Obolus a member of the family LingulidcB : the manner in which the pedicle 

 passes between the beaks being essentially similar to that of Lingula, the structure is 

 rather more solid than that of the last named genus, and from Dr. Carpenter's microscopic 

 examination would appear to be impunctuate ; the muscular impressions though 

 different in their details bear also some analogy to those of Lingula. Professor Kutorga 

 has ably described and illustrated this genus, in his paper on the Siphonotretaeee, wherein 



^ This is the most ancient species at present known, see Professor M'Coy 's paper, in the ' Ann. and 

 Mag. of Nat. Hist.,' vol. viii, p. 405 ; and to Mr. Salter's very interesting observations on the Lowest 

 Fossili/erous beds of North Wales, in the 'Reports of the Brit. Ass.,' for 1852. 



2 Zoologia Specialis, vol. i, p. 274. 



^ Beitrage zur Geognosie der Russischen Reich, 1830. 



* Uber die Siphonotretaeae, Verhandlungen der Kaiserlichen Min. Gesellschaft fUr das Jalir 184". 



