164 DR. T. DAVIDSON ON RECENT BRACHIOPODA. 



Hi/pothyrispsittacea,Fovhes8i}Iaji.\ej,A History of British Mollusca, vol. ii. p. 3 IG, pi. Ivii.figs. 1-3, 1849. 



Rhyncho7iella psittacea, Quenstedt, Handbuch der Petrefakteukunde, pl. 35. fig. 44, 18.51 ; Davidson, 

 Ann. & Mag. Nat. Hist. 2nd ser. vol. ix. p. 374, 18.52 ; L. Barrett, Ann. & Mag. Nat. Hist. 2nd ser. vol. xvi. 

 p. 259, 1855; S. P. Woodward, A Manual of the Mollusca, p. 225, figs. 138 & 189, 1856 ; A. Adams, The 

 Genera of Recent Mollusca, vol. ii. p. 582, pl. cxxxii. fig. 2, 1858; A. Hancock, On the Organization of the 

 Brachiopoda, Phil. Trans, vol. cxlviii., 1858 ; E. Sness, Ueber die Wolinsitze der Brachiopoden, Sitzungsb. 

 k. Akad. Wissensch. Wien, p. 218, 1859 ; L. Reeve, Monogr. of Rhynchonclla, pl. i. fig. 2, 1861. 



Hemithyris psittacea, M'Coy, Synopsis of a Classification of the British Palaeozoic Fos.sils, p. 199, 1865. 



Rhynchonella psittacea, Gwyn Jeffreys, British Conchology, vol. v. p. IGl, 1869, and Proc. Zool. Soc. 

 1878, p. 413 ; Gould, Report on the Terebratulce of Massachusetts, p. 210, fig. 501, 1870. 



Hemithyris psittacea, Dall, Proc. Acad. Nat. Sci. Philadelpliia, 1873, p. 196. 



Rliynchonella psittacea, Davidson, Brit. Foss. Brach. vol. iv. pp. 8 & 16, pl. ii. fig. 5, 1874 ; G. O. Sars, 

 Moll. Regionis Arcticse Norvegiee, p. 9, t. i. fig. 1, 1878; Whiteaves, Canadian Naturalist, vol. viii. 

 no. 8, 1878; G. Dunker, Index Mollusc, maris Japonici, p. 253, 1882; Davidson, Brit. Fossil Brach. 

 vol. v. p. 331 etc., 1884. 



Shell somewhat triangular, globose, broadest anteriorly, tapering posteriorly, lateral 

 margins rounded. Dorsal valve inflated, especially at the umbo, more or less divided 

 into three lobes, of Avbich the central one forms a mesial fold, scarcely defined in some 

 specimens, much more so in others ; front line nearly straight or three-lobed. Ventral 

 valve much less convex than the dorsal one, rather flattened, with a broad, channelled, 

 flattened, longitudinal mesial sinus ; beak sharply pointed, incurved, under which is 

 situated an incomplete elongated foramen, margined anteriorly by the umbo, and 

 laterally by triangular deltidial plates ; beak-ridges not sharply defined ; lateral 

 margins of the valves sinuous, curved in front. Surface of valves radiately and 

 finely striated. Shell-structure fibrous. Valves strongly articulated by curved teeth 

 in the ventral valve, fitting into sockets in the dorsal one. Hinge-plate in the dorsal 

 valve deeply divided, supporting two short, flattened, grooved and curved lamellte. At 

 the bottom of the dorsal valve are seen the quadruple muscular impressions left by the 

 adductor or occlusor muscles, each pair beiug separated by a short medio-longitudinal 

 ridge. In the interior of the ventral valve the teeth are supported by dental plates 

 extending to tlie bottom of the valve, and at their base a semicircular ridge on either 

 side encloses a saucer-shaped depression in which are situated the muscular scars. Close 

 under the beak the peduncular muscles leave a small scar ; lower down and towards 

 the centre of the valve is situated a divided heart-shaped scar due to the adductor or 

 occlusor muscles ; and on each side of these are situated, one above the other, the divari- 

 cator and ventral adjuster muscular impressions. The animal is provided with elongated 

 spiral arms, directed inwards, towards the concavity of the dorsal valve ; alimentary 

 canal terminates behind the insertions of the adductor in the ventral valve ; mantle not 

 adhering, its margin fringed witli a few short setae. Colour bluish or a brown-black. 

 Length 1 inch 3 lines, width 1 inch 1 line, depth 9 lines. 



Rab. Bhijnchonella psittncea is circumpolar in its distribution. It was dredged in 

 Eranklin-Pierce Bay, lat. 79° 25' N., in 15 fathoms, and at Cape Napoleon in 15 fathoms, 

 by Nares's Arctic Expedition in 1875, being in fact the only Brachiopod obtained 

 by the ' Alert ' and ' Discovery ' in those polar regions. R. psittacea abounds in the 



