22 BRITISH TERTIARY BRACHIOPODA. 



Hemithiris psittacea, D'Orb. Considerations Zoologiques et Geologiques sur Ies 



Brach. ; Comptes Rendus de l'Academie des Sciences, 1847 ; 

 et Pal. Franc. Ter. Cretaces, vol. iv, atlas pi. 490, fig. 10 



Rhynchonella psittacea, Woodward. 1851. Manual of the Mollusca, p. 8. 



Diagnosis. Shell of a rounded, somewhat gbbosely triangular shape, compressed 

 laterally ; smaller valve gibbous, with a slight mesial fold often becoming indistinct by the 

 regular convexity of the valve ; larger valve convex, but less so than the smaller one, with 

 a wide, shallow sinus, beginning at a little distance from the beak, and extending to the 

 front; beak acuminated, acute and recurved, leaning considerably over the umbo, and 

 perforated by an elongated foramen extending from under the extremity of the beak to the 

 umbo, which completes the circumference, two narrow deltideal projections laterally edging 

 the aperture. A slight flatness is visible on each side of the beak, the ridges of which are 

 indistinct ; the marginal line of larger valve indents considerably the hinge line of smaller 

 valve near the umbo. 



The surface of the valves are ornamented by a great number of closely disposed small 

 striae, sometimes dichotomising at a short distance from the beak and umbo, also augmenting 

 by the intercallations of smaller costae, from forty-five to fifty in number on each valve ; 

 besides these, numerous lines of growth intersect the longitudinal striae. The internal 

 calcareous appendages in the imperforated valve consist of two small curved lamellae, not 

 exceeding more than one third the length of the shell, to which, in the living state, two 

 free fleshy arms are fixed, and, according to Professor Owen, forming six or seven spiral 

 gyrations, decreasing towards their extremities, which, when completely unfolded, extended 

 beyond the shell to twice its longitudinal diameter. In the interior of the smaller valve a 

 rudimentary septum divides the muscular impressions visible on either side of it. In the 

 larger valve the dental plates are strong, and extend to the bottom of the valve, leaving 

 also between them the corresponding muscular and peduncular impressions. Structure 

 unpunctuated, and formed of minute plates. Colour blackish, and slightly glossy. Length 

 11 ; breadth 10; depth 8 lines. 



Obs. This remarkable Brachiopod has been long known, its animal having been well 

 described by Professor Owen. 1 The structure of the shell has likewise been examined 

 microscopically by Dr. Carpenter, 2 and has been considered a type for the division of the 

 great family of Terebralulte into punctuated and unpunctuated genera. This species is 

 very interesting, inasmuch that it is found recent in our seas, and fossil in our 

 upper tertiary strata. We are indebted to Professor Forbes 3 for valuable information 

 relative to its habitat, as found recent on our coasts. He states, that Mr. Maclaurin 

 procured it from the Berwickshire coast ; 4 also by Laskey, oft' Aberlady Bay ; and in deep 



1 See Professor Owen's Paper, 'Transactions of the Zool. Soc.,' vol. i, 2d part. 



2 See Dr. Carpenter's Report, British Association, p. 18, 1844. 



3 Forbes and Hanley, 'British Mollusca,' vol. ii, p. 339, &c, 1849. 



4 Berwickshire Nat. Club, vol. i, p. 213. 



