CLASSIFICATION OF THE BRACHIOPODA. 103 



Obs. In 1827, Dalman proposed the genus Orthis for a group of shells which he 

 compared to the Scallop, but placed a mark of doubt after his first two types, viz., ? 

 pecten and 0? striatella, his examples being in bad condition, so that he was not certain 

 if they really belonged to the genus; but to his following types he placed no mark of doubt. 

 0. sonata, callactis, calli^ramma, elegantula, &c., must therefore be considered the 

 typical forms of Orthis ; besides which, the first two species mentioned belong to different 

 genera, neither of which agree with such shells as 0. zonata or 0. calli(/ramma. 



The genus Orthis forms a well- characterised natural group, abounding m species and 

 easily recognised. In 1848,^ I stated that the species described by various authors as 

 Spirifer hiforatus or Lynx, and 8p. bilohus or cardiospermiformis, did not belong to the 

 genus Spirifer, but to that of Orthis, since they possess all the essential characters of 

 Dalman's genus, and none of those peculiar to the Belthyrida or Spirifers. My views 

 were adopted by M. de Verneuil,^ D'Orbigny,^ Professor M'Coy,* and Mr. Salterns but 

 Professor King not being convinced of their correctness, proposed, in 1849, the appellations 

 of Platystrophia for 0. hiforata, and Diccelosia for 0. hiloha^ but to which sections 

 the learned Professor does not I believe, at present, attach such great importance. I still, 

 therefore, maintain my first view, M'hich will be better understood by a glance at the 

 respective figures (Pis. VII and VIII). 



Geol. ranye. — Orthis is one of the oldest forms of animal life, having first appeared in 

 the lower Silurian epoch, and continued uninterruptedly to the carboniferous period, above 

 which we are not at present acquainted with any well-authenticated example, although 

 some authors have most erroneously quoted it as occurring in the cretaceous, tertiary, 

 and recent state ; but an examination of the types of those so-called Orthides will soon 

 convince any one that they do not possess the essential characters of the genus. 



Examples: 0. calliyramma,T>Q\..; testudinaria, Dal.; eleyantula, Dal.; biloha, Linn., 

 sp. ; hybrida, Sow. ; rustica. Sow. ; Lewisii, Dav. ; Bouchardii, Dav. ; cequivalvis, Dav. ; 

 Michelini, Lev. ; opercularis, Vern. ; reversa, Salter ; Gervillei, Def., sp. ; palliata, Barr. ; 

 mulus, Barr. ; Beaumontii, Vern. ; obtusa, Pander, sp. ; Diimontieri, Vern. ; striatula, 

 Schl., sp. ; Lynx, Eich. ; biforata, Schl. ; resupinata, Martin, sp. ■'} Lyelliana, De 

 Koninck ; &c. 



1 Bull, de la Soc. G^ol. de France, vol. xxi, 2d ser., 1848. 2 Hjij. 



^ Prodrome de Paleontologie Stratigraphique, vol. i. 

 * British Palaeozoic Fossils of Mus. Camb., 1852. 



5 Mem. Geol. Surv., vol. ii, part 1, 1848. 



6 A Monograph of British Permian Fossils, 1849. 



7 Among the Carboniferous Brachiopoda in the Museum of the Geol. Soc, may be seen two very 

 remarkable ventral or dental valves, which had been discovered by Mr. J. Yates, at Llanymynech, 

 and which I am inclined to believe may have belonged to a species of Orthis, bearing great external 

 resemblance to that form known by the name of O. resupinata, Martin, sp. These valves are most 

 remarkable from their very large and deep cardinal and adductor muscular impressions, the last mentioned 



