MONOGRAPTUS. 467 



length is involved in the barb, approach rather in this respect some of the members 

 of the preceding group (such as M. Clingani), but show always too high a proportion 

 of isolation for inclusion in that group, and they are, therefore, considered as being 

 rather closer to the members of Group V. 



The polyparies are almost always curved, but the amount of curvature 

 varies greatly. 



The species included in this group may be subdivided into sections and sub- 

 sections according to the uniform or bi-form type of the theca?, and the curvature 

 of the polypary. 



A. With bi-form thecae. 



(a) The polypary has spiral curvature. Type : Monograptus convolutus. 

 M. decipiens, M. urceolus. 



(b) The polypary has dorsal curvature. Type : Monograptus triangulatus. 

 M. triangulatus var. major, M. rait zhaifbien sis, M. denticulatus. 



B. With uniform thecae. 



(a) The polypary has spiral curvature. Type : Monograptus spiralis. 



M. proteus, M. delicatulus, M. iuvolutus, M. circularis. 

 (/>) The polypary has dorsal curvature. Type : Monograptus communis. 



M. communis var. rostratus, M. fimbriates, var. similis, M. planus, 



M. intermedins. 



(c) The polypary has dorsi-ventral curvature. Type : Monograptus 

 cf. elongatus. 



VI. A. (a) : Monograpti in which the thecae are bi-form and the polypary has spiral 



curvature. 



Monograptus convolutus (Hisinger). Plate XL VII, figs. 1 a — (/. 



1837. Prionotus convotutus, Hisinger, Letli. Suec. Supplem., p. 114, pi. 35, fig. 7. 

 1868. Graptolitlius convolutus, Carruthers, Geol. Mag., vol. v, p. 127, pi. v, fig. 1. 

 1881. Monograptus convolutus, Tullberg, Grapt. desc. by Hisinger, p. 14, pi. ii, figs. 13 — 16. 

 1892. Monograptus convolutus, Torncpuist, Siljansomrad. Grapt., ii, p. 30, pi. iii, figs. 5 — 11. 

 1897. Monograptus convolutus, Perner, Grapt. de Bolicme, p. 13, pi. xii, figs. 26 — 29 ; pi. xiii, fig. 41, 

 text-fig. 10. 



Polypary often of considerable size and length, coiled into a flat spiral, except 

 at the distal extremity which is merely arcuate ; slender, but widening 

 gradually for the first few whorls, then maintaining a constant breadth of 

 3 mm. for the remainder of its extent. Thecae ten to seven in 10 mm., 

 on the convex margin ; those of the proximal portion of the narrow, 

 isolate Rastrites type, those of the distal portion triangular, in contact onlv, 



