12 BRITISH PERMIAN BRACH10P0DA. 



Family— SPIRIFERID^E. 



In the French edition of ray General Introduction, published in vol. x of the 

 'Transactions of the Linnean Society of Normandy/ I have provisionally divided the 

 family SPIRIFERIDvE into three principal genera— Spirifera, Sow., Athyris, M'Coy 

 = Spirigera, D'Orb., Atrypa, Dalman ; and into six sub-genera — Cyrtia, Dalman, 

 Spiriferina, D'Orb., Suessia, E. Deslong., Betzia, King, Merista, Suess, and Vncites, Defr. 

 But before a genus or sub-genus can occupy a definite and permanent position in science, 

 it is necessary to be acquainted with all its characters, both internal and external, and to 

 have appreciated these characters so as to be able to compare them to those of other genera 

 in the same family. 



Some short time since only have all the internal arrangements of the three above- 

 named genera been completely ascertained, that of Athyris in particular having resisted 

 for many years the most persevering researches. 1 The differences presented by these 

 genera are most satisfactory ; they represent three well-defined types, around which certain 

 modifications of comparatively smaller value naturally converge. Of the six sub-genera, 

 Spiriferina alone has been thoroughly investigated ; but of the others much still requires 

 to be learnt before the value of their respective characters or distinctions can be satisfac- 

 torily established. MM. Suess and Deslongchamps|have already done much towards the 

 elucidation of the interiors of Merista and Suessia, but we are not yet in a condition to 

 furnish a completely restored illustration of all tbe parts of which their interior is com- 

 posed. Merista was in all probability closely related to Athyris, and what little we know 

 of Suessia would appear to denote that it possessed a very remarkable interior, since, with 

 the external shape of a true Spirifer, it presents many dissimilarities in its internal orga- 

 nization. In Suessia the two branches which constitute the first spiral coils are united by 

 a transversal, shelly band, from the centre of which proceeds another short lamella, which 

 is directed towards the bottom of the valve. The species that compose this small group 



there appears to be no difference between them in their histological perforations." ('Annals and Mag. of 

 Nat. Hist.,' vol. xvii, 2d series, March, 1856.) 



In speaking of T. sacculus, Professor M'Coy states ('British Palaeozoic Fossils,' p. 411) that "several 

 writers mention their inability to distinguish this species from some of the varieties of Seminida elongata 

 and S. sufflata of the Permian rocks ; but specimens perfectly identical in form and size may be readily 

 distinguished by a small but distinctly marked upward wave in the front margin towards the anterior valve 

 in the Permian fossil, while the margin of the Carboniferous species is nearly or quite horizontal. In 

 iS. svfflata, also, the mesial septum is much longer and more strongly marked in the receiving valve, 

 extending to within one third of the length of the front margin." 



1 When I published my Introduction in the first volume of this work, the character of Athyris had not 

 been fullv ascertained. 



