180 SUPPLEMENT TO THE BRITISH 



carinated dorsal valve, much incurved beak, and very sharply defined beak-ridges. W. 

 Jlorella is a more elongated form, with a much less convex dorsal valve than W. carinata. 

 Nevertheless, as observed by Mr. E. Deslongchamps, in comparing them one with another 

 we cannot avoid tracing a kind of connection in a series of forms, but slightly modified, 

 succeeding each other as we rise in the series of Jurassic deposits. I entirely concur in 

 the view expressed by my distinguished friend, and especially in his conclusion that the 

 study of the Brachiopoda confirms us more and more in our belief as to the unlimited 

 variability of the species, that we cannot admit that each period sees the first appearance 

 of the species it contains or their sudden disappearance just at the precise moment when 

 so many others make their first appearance. I might likewise add that, in many cases, 

 the prevalent desire of limiting the practical range of species to their supposed limited 

 horizons, overlooking their essential characters and variability, has led to the raising to the 

 rank of distinct species mere variations or slight modifications in shape of no real specific 

 value. This fact is amply verified by the study of the W. resupinata group, and is even 

 more remarkable in that multitude of perplexing and so-termed distinct species (?) that 

 have been proposed for the T. biplicata group. Mr. J. E. Walker considers, however, that it 

 is advisable to give a name to a well-marked variety when it is constantly found in a given 

 geological horizon, although it maybe connected by rare forms with other species ; and also 

 for the purpose of limiting the extent of variation of a form bearing the same name, so 

 that there can be no doubt which variety is referred to when it is stated to occur in a 

 certain district. 



W. carinata is not very uncommon at Bradford Abbas and Broadwinsor in Dorset 

 and Somersetshire. Some specimens are somewhat truncated at the front margin (Dav., 

 Ool. Mon., PI. 4, fig. 14). 



Two varieties of W. carinata may be recorded : — 



166. Var. Mandelslohi, Oppel. Dav., Sup., PI. XXIII, figs. 16—18. 



Tebebratcla Mandelslohi, Oppel. Die Jura-Form., p. 495, 1857. 



— caeinata-alveata, Quenstedt. Petrefactenkunde Deutschlands Bra- 



chiopoden, p. 349, pi. xlvii, figs. 47 — 50, 1871. 



— (Waldheimia) Mandelslohi, E. Deslongchamps. Brach. Jur., p. 295, 



pi. lxxxv, figs. 3—5, 1874. 

 Waldheimia — Dav. Proc. of the Dorset Nat. Hist. 



and Antiq. Field Club, pi. iii, 

 fig. 8, 1877. 



This variety, as observed by Mr. E. Deslongchamps, approaches very nearly in shape 

 to W. carinata, of Lamarck, and, indeed it appears to me to be nothing more than a wide 

 variation in shape of the Lamarckian species. If one gives a glance at Deslongchamps' 

 figure of a wide form of W. carinata, ' Brach. Jur./ PI. 62, figs. 7 and 10, and then 



