2 OEDOVICIAN AND SILURIAN BELLEROPHONTACEA. 



reference must be made to the work of Clarke/ Knocl,^ Spitz/ and others in 

 connection with the usage of the generic names. 



We need not here concern ourselves with the earlier views on the classification 

 of the group, or wnth the discussion of its true zoological affinities and position. 

 If we follow the last edition (1913) of Zittel-Eastman's ' Text-book of Palason- 

 tology ' we place it in the vicinity of the Pleurotomariidas. Ulricli and Scofield 

 instituted a separate sub-order for the group and called it Bellerophontacea, and 

 this seems a convenient, if not quite natural, method of designating an assemblage 

 of gastropods possessing certain distinctive features in common. 



The further division into two sections or groups characterised by the absence 

 or presence of a slit-band, was adopted by Perner (oj). cif., pp. 58, 59), and seems 

 more suited to the present imperfect state of our knowledge than the elaborate 

 arrangement into families which is employed in Zittel-Eastman's ' Text-book.' 



The group-names chosen by Perner for the two sections are unfortunate, and 

 do not express the fundamental feature on which his classification is based. If 

 names are required we might suggest Integridorsata as more suitable than his 

 Cyrtolitoidea, and Fissidorsata in place of his Bucanioidea, for neither Gyrtolites 

 nor Bucania are the originally described or characteristic representatives of the 

 groups. A third section or sub-group is required for those in which the slit is 

 replaced by a chain of pores, and the name Terebridorsata might be applied to it. 



The following are the British Genera so far recognised from Ordovician and 

 Silurian beds : 



GrEOUP I. 



Integridorsata (dorsum without median fissure, band, or row of perforations). 



Sinuites. Cyrtolites. 



Sinuitojjsis. Bucaniella. 



Oxydisexis. 

 Geoup II. 



Fissidorsata (dorsum with median fissure or band). 



Bellerophon sens. str. Temnodiscus. 



Bucania. Bucaniopsis. 



Kokenospira. Cymbularia. 



Tetranota. Zonidiscus. 



Conradella. ( = PhragmolUes) \_Salpingostoma.] 



Sub-Geoup II a. 



Terebridorsata (dorsum with median row of perforations). 



Trematonotus, Phragmostoma . 



Incertse sedis. Carinaropsis. 



1 Clarke, "Palaeozoic Faunas of Para" ('Arch. Mus. Nac. Rio de Janeiro,' vol. x, 1899), English 

 edition, 1900, pp. 34—43 ; " Foss. Devon. Parana " (' Mon. Serv. Geol. Miner. Brasil,' vol. i, 1913, Eio 

 de Janeiro), pp. 165 — 175. 



2 Knod, ' Neues Jahrb. f. Miner.,' suppl. vol. xxv (1908), pp. 503—508. 



^ ^ Spitz, " Gastrop. Karnischen Unterdevons " (' Beitr. Palseont. Geol, Oesterr. u. Orients,' vol. xx, 

 1907, p. 124). 



