22 BRITISH CRETACEOUS BRACHIOPODA. 



shaped lamellae described, we observe two upper anchor-like lamella?, situated parallel to 

 the under ones; while in Bouchardia the under ones are completely wanting. In Waltonia, 

 on the contrary, we have hitherto observed only the lower ones. 1 



Since the period of Mr. Bouchard's and my own publications on the genus and species 

 under notice, I have assembled a very extensive suit of British specimens, which enabled 

 me to collect some additional facts regarding the external shape and variations sometimes 

 assumed by this interesting little shell, which does not seem to have ever exceeded much 

 more tban 5 or G lines in length. The shape of the beak, as well as the form of the smaller 

 valve, often producing great variations in its external aspect ; in general, the smaller valve 

 presents a slight longitudinal depression appearing at some distance from the umbo, and 

 extending to the front, the beak being more or less incurved ; but from several remarkable 

 specimens discovered by Messrs. C. B. Rose, Fitch, Catt, Woodward, and myself, it appears 

 that in some cases the smaller valve becomes more or less convex without depression, the 

 beak being almost straight, and exhibiting a greater or less developed area and foramen, as 

 may be seen from the series of illustrative figures in Plate II, which I have selected out of 

 a vast number of specimens, to show the passages of form ; 2 in figs. 1 and 2 the beak is 

 much recurved, and the smaller valve more or less concave ; in fig. 4 it is less so, the 

 foramen being more visible ; in 5 and 6 the smaller valve is slightly convex, the beak 

 hardly recurved, and in the two extremes of 7 and 8, this last is almost straight, showing 

 a large area and foramen. On closely examining the latter exceptional variations or 

 malformations, I soon became convinced that they arose from local causes, and especially 

 from the shortness of the pedicle muscular fibres, forcing the beak and area to lie so close 

 to the object of attachment, as to prevent the curvature of the beak ; this is likewise proved 

 by the umbo of the smaller valve in these specimens being worn by friction, as we remark in 

 many specimens of Argiope, &c. ; in very young individuals the beak is also almost straight, 

 becoming recurved at a more advanced period of growth. Magas pumilis is circular, oval, 

 or more or less elongated, as may be perceived from figs. 9, 10, 11. Sowerby's 

 illustration and type of Magas does not show a very recurved beak, which at the time we 

 first described the genus we believed to be a mistake, owing to the Meudon specimens not 



1 While looking over the valuable collection of M. Deshayes iu Paris, I was agreeably surprised to find 

 in one of his drawers the interior of a Cretaceous species, from the Tourtia of Belgium, described by 

 Viscount d'Archiac in the second volume of the 'Mem. de la Soc. Geol. de France,' p. 333, pi. xxii, fig. 4, 

 under the name of Terebratula orthiformis, and ater, by M. de Koninck, under that of Orthis millepunctata ; 

 in this shell we find the same arrangements as in Magas, to which genus the species above noticed 

 will have to be referred. Unfortunately, the upper pair of lamellae are imperfect in M. Deshayes' 

 specimen. 



2 Mr. Woodward, in his ' Synoptical Table of British Organic Remains,' 1830, p. 22, mentions three 

 species of Magas, M. pumilus, Sow., M. magna, and M. punctata, all from the chalk of Norwich ; but as 

 these last two are MS. names, unaccompanied by figure or description, we cannot offer any positive opinion 

 on the shells intended as types, but it is probable, if not certain, that they were made out of the extreme 

 shapes of Magas above noticed and figured in our plate. 



