20 BRITISH PERMIAN BRACHIOPODA. 



exists relative to the question of absolute identity, it will be preferable for the present to 

 allow both Schlotheim's and Sowerby's shells to retain their distinctive appellations. The 

 Trigonostrata Jonesiana of King appears to Messrs. Howse, Kirkby, and myself to be only 

 a more rounded form or variety in shape of Sp. multiplicata, and was so considered by 

 Professor King himself until 1850, when he removed it on account of its lesser width, 

 more prominent umbone, and higher area ; the ribs being also more evenly rounded and 

 at a greater distance from each other, the median one on the smaller valve more evenly 

 convex, and its corresponding furrow in the opposite valve more evenly concave ; but these 

 differences brought forward by that author seem to be those common to many young 

 individuals of the Sowerby shell, and cannot, in my opinion, claim a specific distinctive 

 denomination. 



Sp. multiplicata is not very rare in the shell and compact limestone of Tunstall and 

 Humbleton hills, and at Dalton-le-Dale. 



Genus — Athyris, M'Coy. = Spirigera, D'Orb. 

 Spirigera. Introduction, vol. i, p. 87, pi. vi, figs. 65 — 70, 79, 1853. 



05s. With the desire to obviate and correct a zoological misnomer, I proposed, in 

 1853, to adopt the generic designation Spirigera, D'Orb., for such shells as T. con- 

 centrica, pectinifera, de Boissyi, &c, and to retain that of Athyris, M'Coy, for such as 

 T. tumida, Herculea, scalprum, &c. But this arrangement not having met with the entire 

 approval of several distinguished friends, I have willingly complied with their desire by 

 re-establishing Athyris as typified by A. concentrica, pectinifera, &c, while for such shells 

 as T. tumida, Herculea, &c, that of Merista, Suess, has been adopted. 1 The external 

 and some of the internal characters are already well known ; but it is not until lately that 

 the arrangement, attachment, and connecting process of the two spiral cones has been 

 discovered, and which will be found fully described under A. pectinifera. 



In Prance and in Germany the term Spirigera is generally adopted and preferred to 

 that of Athyris, and I cannot but say with good reason ; but the law of priority obliges us 

 to retain that of Athyris as a mere generic appellation, for it would not be just or fair to 

 repudiate that of M'Coy on account of its erroneous interpretation or etymology, as long as 

 so many other equally objectionable names are allowed currency in science. 



1 French edition of my General Introduction, in vol. x of the 'Transactions of the Linnean Society of 

 Normandy.' Also in the German edition, published by M. Suess. 



