DR. T. DAVIDSON ON EECENT BEACHIOPODA.. 93 



Terebratula rhombea, Philippi, Archiv fiir Naturgesch. Jahrg. xi. Bd. i. p. 59, 1845. 



Terebratula flexuosa, G. B. Sowerby, Thes. Concli. i. p. 317, pi. Ixix. figs. 23,24, 1846. 



Terebratdla dorsata, E. Suess, Ueber die Wohnsitze der Brachiopoden, Sitzungsb. k. Akad. Wis- 

 sensch. Wien, Bd. xxxvii. p. 208, 1859. 



Terebratula {Terebratella) stiffusa, L. Reeve, Conch. Icon. pi. v. fig. 18, 1800. 



Terebratula {Terebratella) Magellanica, L. Reeve, Coucb. Icon. pi. v. fig. 21, 1860; and Ann. & Mag. 

 Nat. Hist. 3rd ser. vol. vii. p. 176, 1861. 



Magasella flexuosa, Dall, Amcr. Journ. of Conch, vol. vi. p. 135, 1870; and Proc. Acad. Nat. Sci. 

 Philadelphia, p. 189, 1873 ; Davidson, Report on the Brachiopoda, Voyage of H.M.S. ' Challeuger,' Zool. 

 vol. i. p. 46, pi. iv. fig. 5, 1880. 



Shell somewhat subtetragonal, about as broad as long, yellowish or light I'cddish 

 brown, widest near the hinge-line, tapering anteriorly, lateral and frontal margins 

 flexiious. Dorsal valve moderately convex, longitudinally depressed mesially from about 

 half the length of the valve to the front. Ventral valve deeper than the dorsal one, 

 longitudinally keeled. Beak short, incm'ved and truncated by a rather large incomplete 

 foramen, completed by a small portion of the umbo of the dorsal valve, and by rather 

 large lateral slightly-separated deltidia ; l)eak-ridges well defined, leaving a flattened 

 space or false area between them and the long obtusely angular hinge-hnes. Surface of 

 both valves ornamented with from thirty to forty radiating diverging angular ribs, 

 ciu'ving to the lateral margins, straight along the middle, with shorter ribs interpolated. 

 Shell-structure traversed by small canals. In the interior of the dorsal valve the loop 

 is doubly attached. Mesial septum large, abruptly elevated at its anterior extremity, 

 extending from under the hinge-plate to about two thirds of the length of the valve. 

 The upper edge of the septum commences by presenting a gentle curve iu the shape of 

 a half-circle, then by an oblique nearly straight line reaches its greatest elevation, and 

 again assumes an almost straight line, to be followed by an abrupt inward curve until 

 it reaches near to the bottom of the valve, where it gradually terminates by another 

 gentle curve. The greatest elevation attained by this vertical plate in a specimen ten 

 lines in length was four lines. The principal stems of the loop at about two thirds of 

 their length increase in breath and become fixed to the sides of the septum near the upper 

 portion of the first slope, and, after proceeding a little further, become reflected, 

 the anterior portion of the septum being prolonged for some distance in front of them 

 (PL XVII. fig. 5). The muscular impressions are rather large, and are seen on the 

 bottom of the dorsal valve on each side of the septum. The ribs observable on the 

 surface of the valve are reproduced on their interior surface. Length and breadth about 

 1 inch, depth 6 lines. 



Hub. Straits of Magellan, in the vicinity of Port Famine ; Orange Harbour ; 

 Gulf of Patagonia, near Cape Horn, and not far from the Falkland Islands, iu 1450 

 fathoms ; Port Stanley, at a depth of 5 to 12 fathoms (' Challenger ' Expedition). 

 Captain P. P. King, K.N., the first discoverer of the species, states, " this shell was 

 dredged in the Bay of Port Famine, attached to stones ; it is a common shell in the 

 Straits." 



Ohs. In external shape this shell nearly approaches Terebratella dorsata, Gmelin, 

 and, indeed, L. Reeve places it among the synonyms of tho last-named species. It differs, 



13* 



