DR. T. DAVIDSON ON EECENT BEACHIOPODA. 165 



Norwogian Seas, from Drontheim to the North Cajie ; off Shetland ; Grand Greve, Gaspav 

 Bay, Canada East ; Unalashka to Shumagins in the Aleutian Chain (Dall) ; Banks of 

 St. Margaret Bay; Russian Lapland to Sitka; from Behring Strait to Japan in North 

 Pacific; in the Gulf of St. Lawrence, Canada, and in several other places. 



Fossil. It occurs in the Upper Tertiaries of Great Britain, Ireland, Scandinavia, Canada, 

 Sicily, south of Spain, &c. 



Obs. Until 1S()9, when Fischer de Waldheim proposed his excellent genus Ithijncho- 

 nella, the shell under description had been described under the fancy and generic names 

 of ''Bee de perroquet,'" Anomia and Terebratiila; since then sometimes by those of 

 Hemithyris, Hypothtjris, Lampas, and Gi/pidea ; but Fischer's name Rhynchonella is the 

 generic designation by which the shell has been generally known, and that which should 

 hold priority over all others. 



Rhynchonella psUtacea does not vary very much in external shape ; young specimens 

 are, however, more triangular, less convex, and with a more elongated triangularly shaped 

 beak. The dorsal valve in some adult examples is uniformly convex, while others show 

 a well-defiued mesial fold. The intimate structure of the shell of Rhynchonella has been 

 carefully studied, described, and illustrated by Dr. W. B. Carpenter in various jiapers. 

 He says : — " No one who examines the shells of the Recent Rhynchonella psittacea and 

 Rh. nigricans, even in the most superficial manner, can have any hesitation in recognizing 

 the entire absence of the superficial ' punctuations ' which mark the orifices of the shell- 

 canals in the recent species of TevebratuUdce; and the most careful microscopic exami- 

 nation of these sections of the shell, taken from any part and in any direction, does but 

 confirm this conclusion. ... In all other respects the intimate structure of the shell cor- 

 responds precisely with that of Terebratulidce ; but it may be mentioned that the prismatic 

 laminoD are less adherent to each other than in the perforated shells, so that they are 

 readily split asunder." (' On the Intimate Structure of the Shells of Brachiopoda,' 

 Palseontological Society, p. 35, 1851.) 



The animal of R. psittacea and its anatomical characters were carefully described 

 by Richard 0^ven in 1833, and especially by Albany Hancock, in his admirable 

 memoir " On the Organization of the Brachiopoda," in the Philosophical Transactions of 

 the Royal Society for 1858. 'Wq arc likewise indebted to Prof. T. H. Huxley for several 

 valuable anatomical details published in vol. vii. of the Proceedings of the Royal Society 

 for 1854, as well as to several other distinguished zoologists. In 1835 Quenstedt, in 

 Wiegmann's Archiv, Bd. ii. p, 220, founding his views on very precise reasons derived 

 from the mode of attachment of the valves in Rhynchonella psittacea, pointed out the 

 two orders of muscles, of which one closed, while the other opened the valves. 



Mr. Lucas Barrett informs us that he found Rhynchonella psittacea A-ery difficult to 

 exaiuine, the animal being extremelv timid and closed its valves on the slightest move- 

 ment ; the coiled arms are extended, so that the cirri come as far as the margin of the 

 shell, but it never protruded its arms *. 



In Rhynchonella psittacea, as well as in other species of the genus, the elongated spiral 

 appendages are supported at their origin only by two short, curved, projecting calcareous 



* Annals & Mag. Nat. Hist. 2nd ser. vol. xvi. p. 259, 1855. 



22* 



