xxiv BRITISH GRAPTOLITES. 



brandies. Tlicse smaller divisions constitnte true " cells." In tlie widest part of 

 the polypary the branches may split as often as fonr or five times. Suess admits 

 that it is somewhat difficult to understand how the transverse walls bounding the 

 "cells" were produced. The genus lictloHies is distinguished from PdaJolithus 

 {Dlprion, Barr) by having its secondary branches united by a distinct cell system 

 instead of by a membranous substance. 



Descrljyfion of Sj)eci<'S. — In addition to (1) RclLulitcs Gcluitzlanns (which Suess 

 regards as synonymous Avith Fuco'uJes (Iciitdliix, Brong., (Jr. pridis, Gr. scalaris, 

 Gr. folia cea-f, Gr. secahnui^, and other biserial forms) Suess describes and figui-es 

 a new form under the name (2) Retiolitrs grandis. The individuality of this 

 last-named species was not recognised by subsequent writers until a comparatively 

 recent date, when Tullberg made it the type of a new genus, Stomatofjraptiis, but 

 his interpretation of its structure is very different from that of Suess. Suess con- 

 sidered it to be distinct from liet. Geinitziaiuis on account of its larger size, the 

 peculiar form of the outer margin, and the small vertical distance apart of the 

 secondary l)ranches ; while Tulll)erg distinguished it because of its median row 

 of " pores." 



Under the description of his new genus Petalolithus Suess notes the prolonga- 

 tion of the solid axis at both ends, and agrees Avith Barrande that it is very probable 

 that the cells have fallen off these naked prolongations. He makes a great point of 

 the alternate or opposite position of the secondary " branches," and thinks it is due 

 to subsequent movement or disturbance. He considers that it is possible to recognise 

 in Petalolithus something akin to the cell system in RefioJiies, and suggests that in 

 Petalolithus " those parts which take the ])lace of the cell system in Rrliulitc-^ 

 consisted of a skin-like substance provided with stomata (?)." 



He divides tlie forms assigned to PetaloUiJtiis into two groups : 



{(i) those in which there is a decrease in width at both ends of the polypaiy, 

 l)roducing a characteristic oval shape ; 



(b) those in which the distal walls are parallel. 



The following species of Petalolithus are descriljed and figured : 



(3) P.imlmeus; (4) P. ovatas ; and a new species, (5) /'. parallelo-costatus. 



The structure of the genus Graptoli.fluis (Monopruui) is next discussed, and he 

 considers that the axis in Grujifollfhus is tulje-like, and not solid as Barrande had 

 stated. 



Ill his first groiqi oF the genus Grapiolitliiis Suess includes forms like Vrioiiotas 

 grjiiiiiiis, Gr. ramosiis, etc. (which, according t(j him, had tlie power of branching 

 dichotomously), and describes (0) Gr. jiriodoit ; (7) Gr. hvlicinlrus ; (8) Gr. 

 ,^('rr<iliis (which he l)elieves to be identical with Gr. (leiitfifiis, Gr. Rnemeri, 

 and (Ir. Idhis); (9) Gr. teslls (the structure of the a])erture and spines of 

 whieli he descrilies in great (h'tail); (1(>) Gr. hvrl.s (Hall) (Suess' figure of tliis is 

 possibly a l)ranclied form— a Cijrhiijrapl us,— ])nt (piite unidentifial)le from his 



