BRITISH TERTIARY BRACHIOPODA. 



Genus — Argiope, Deslongchamps. 1842. 

 Megathiris, D'Orb. 1847. 



Shell inequivalved, variable in shape, semi-orbicular, quadrate, or transversely oval. 

 Valves unequally convex, smooth, or variously ribbed. The larger valve deep, beak 

 produced with a large depressed triangular area ; foramen large, completed by the umbo 

 of smaller valve, which generally becomes indented from the shortness of the peduncule, 

 forcing the beak and umbo to lie close to the rock coral or other objects to which it is 

 attached, and thus wearing by friction that portion of the shell; structure strongly 

 perforated; margin thickened and granulated. Hinge-line straight ; valves articulating by 

 means of two single teeth in the larger valve, and corresponding sockets in the smaller 

 one. Interior of the smaller valve furnished with a central septum, and sometimes with 

 one or more lateral septa, radiating from beneath the muscular fulcrum, and terminating 

 at some distance from the margin in elevated processes. Apophysary system consisting of 

 a distinct loop originating at the base of the dental sockets, and furnished with converging 

 processes ; the loop is folded into two or more lobes, occupying the interspaces of the 

 radiating septa, to which they adhere on their inner sides. 



05s. The shells composing this genus were first separated from Terebratula by 

 M. Deslongchamps, 1 who pointed out its principal differences and affinities to Thecidea, 

 the recent Anomia decollate/,, Chemnitz, or detruncata, Gmelin, being named as the type ; 

 later M. D'Orbigny (probably unacquainted with M. Deslongchamps' claims of priority) 

 proposed likewise to separate the shells in question from the Terebratulse under the generic 

 name of Megathiris f since that period the genus has been re-described by Professor 

 Forbes, 3 who, unacquainted with M. Deslongchamps' priority, adopted M. D'Orbigny's name. 

 It is well figured in several works ; 4 but on the most important character of the genus 

 authors have not yet agreed, namely, if the shell was provided with fleshy arms or not. 

 M. D'Orbigny and Dr. Philippi are stated to have examined the animal anatomically, 

 and to have found none, while Professor Forbes, who has had the same advantages, 

 affirms the animal to be possessed of contorted spiral arms fixed to the margin of the 

 apophysary septa above described, and to the cardinal teeth. 5 Mr. J. E. Gray 6 places this 



1 'Mem. de la Soc. Linn, de Normandie,' vol. vii, p. 9, 1842. M. Deslongchamps' detailed paper 

 appeared in the ' Bull, de la Soc. Geol. de France,' vol. vii, 2d ser., p. 65. 



2 'Comptes Rendus Hebdomadaires de l'Academie des Sciences,' August, 1847. Also in the 'Annales 

 des Sciences Nat. Zool.,' torn, viii, p. 241, 3d sec, 1847 ; and ' Palseontologie Francaise Terrains Cretaces,' 

 vol. iv, p. 146, 1847. 



3 Forbes and Hanley, 'British Mollusca,' vol. ii, 1849. 



* In 1785, by Chemnitz, pi. lxxviii, fig. 705; by Sowerby, 'Thesaurus Conchyliorum,' pi. lxxi, 

 fig. 70, &c. 



5 Since writing the above, Professor Forbes informs me that it must have been a small T. seminulum he 

 examined, and not an Argiope. 6 J. E. Gray, 'Annals of Nat. Hist.,' vol. xiv, pp. 271 — 9. 



