MAGAS. 21 



the insertion of which at the bottom of the valve having prevented the calcareous 

 deposition extending over the space occupied by the muscular fibres ; on either side, at 

 the base of the septum in smaller valve, are seen two muscular impressions, corresponding 

 with those just described in the larger valve, but of much smaller dimensions ; the valves 

 articulate by means of two strong teeth in the larger, corresponding with sockets in 

 smaller valve, their separation becoming impossible without fracture. Dimensions variable; 

 length 4, depth 3 lines. 



Obs. Sowerby wisely created this genus in 1818, by observing that its internal 

 organisation differed materially from that of other Terebratuliform shells ; he states : " In 

 the middle of the shell rises a thin longitudinal septum, reaching from one valve to the 

 other, the upper part of it is perpendicular; on each side are two shelf-like appendages, 



one over the other, the upper ones united by slender processes to the hinge The 



resemblance of the arched septum to the bridge of a violin has suggested the generic name; 

 to which valve this septum is attached I have not been able to ascertain, because I could 

 not open the shell without breaking it." In 1845, having received from my friend, the 

 late Mr. Duval, a great number of perfect specimens of this species, derived from the 

 Upper Chalk of Meudon, near Paris, — M. Bouchard and myself proceeded to develope and 

 examine the internal structure, which we fully described and illustrated two years after in 

 the 'Bull, de la Soc. Geol. de France,' vol. v, 2d ser., p. 139, pi. ii, principally on account 

 of the imperfect figures given by M. D'Orbigny m his 'Pal. Francaise,' proving that that 

 author had not been as fortunate as ourselves in finding out the exact disposition of the 

 internal apophysary system ; the upper anchor-like lamellae having been omitted and 

 unmentioned in the description which appeared long after the publication of our paper. 

 From observation, we were enabled to clear the doubts expressed by Sowerby, showing 

 that the septum was attached solely to the bottom of the smaller valve. Since 1818, this 

 species has often been confounded and misunderstood by various authors, such as 

 Baron von Buch, Lamarck, and others. It is, however, most beautifully and clearly 

 distinguished from all other Brachiopoda by its internal organisation, approaching to the 

 only two genera, Bouchardia 1 and Waltonia, 2 proposed by myself some time back, these 

 forming, along with Magas, a small family, comprising but few species. From Bouchardia 

 and Waltonia, Magas differs in the form of its beak, foramen, and teeth; in Bouchardia the 

 foramen is completely surrounded by the substance of the shell, and separated from the 

 umbo without deltideum ; while in Waltonia the position of the foramen, deltideum, and 

 umbo is similar to that of the genus Terebratulina ; this last, however, approaching more 

 to Magas by the simplicity of its hinge, which is remarkably complicated in the genus 

 Bouchardia. Besides these particular family characters, we find the same central, 

 elevated septum, but different in its details. In Magas, in addition to the two riband- 



1 'Bull, de la Soc. Geol. de France,' vol. vii, 2d ser., p. 62, pi. i, figs. 1— G, 1819. 



2 Davidson, "On the Genus Waltonia," 'Annals and Mag. of Nat. Hist.,' vol. v, 2d ser., 1850, pi. xv, 

 fiK. 1. 



