544 C. Lapworth — On Scottish Monograptidce. 



Fig. 7. Large form of simple coccolith, showing superficial ornamentation of the 



annulus. 

 Figs. 8 to 13. Coccoliths exhibiting the successive stages in which the central area 



becomes subdivided. 

 Fig. 14. Fragment of a complex coccolith included in a glauconitic granule. 

 Figs. 15 to 18. Various stalked forms of coccolith. 

 Fig. 19. A variety of Fig. 9, granulated at the margin. 

 Fig. 20. Membranous film left after the solution of a form like Fig. 8. 

 Figs. 5 to 20 are magnified from 1500 to 2000 diameters. 



III. — N Scottish Monograpttd^. 



By Charles Lap worth, F. G. S. 



[Concluded from page 5^1 .) 



§ ^IIT. 

 Genus Cyrtograptus, Carrutliers. 



This genus was founded by Mr. Carruthers to include those com- 

 pound forms of monoprionidian GraptoUtes in which the polypary 

 is unilateral, growing from the initial point in one direction only. 

 There can be no hesitation in regarding it morphologically as a 

 branching Monograptus ; its mode of development, the characters of 

 its hydrothecEe, and its geological distribution, all pointing unmistak- 

 ably in this direction. It is also very variable in its mode of branch- 

 ing; and occasionally simple examples are met with, un distinguish- 

 able in every respect from typical specimens of Monograptus. This 

 negative evidence is, however, of no great weight, as these examples 

 previous to fossilization may have been deprived of the branches 

 they once possessed. Unlike Monograptus, the species of this genus 

 are few in number, and even individuals are of rare occurrence. Ee- 

 collecting, however, the fragmentary state in which all the forms of 

 the present family are preserved to us, and the impossibility of iden- 

 tifying a species of Cyrtograptus unless we possess unequivocal evi- 

 dence of the compound character of the polypary, it may be regarded 

 as certain that our present scanty list will be greatly augmented in 

 the future. 



35. Cyrtograptus Carruthersi, sp. nov. Plate X. Figs. 6a-c.^ 



Polypary unilateral, compound, monoprionidian. Principal branches 

 long, slender and flexuous, originating similar secondary and simple 

 branches at distant intervals. Hydro thecas 16 to the inch : conical, 

 adnate, in contact only ; apertural margin of each inclined : denticle 

 mucronate, conspicuous. 



The principal branch exhibits the peculiar circinate proximal 

 termination so frequent in the allied genus Monograptus, and is more 

 or less curved throughout the whole of its extent. Extremely 

 slender at its origin, it almost insensibly expands to the normal 

 diameter of one-twentieth of an inch, including the projection of the 

 hydrothecse. As a rule the polypiferous margin is that of the outer 

 edge of the curve, but great irregularity in this respect is caused 

 by the frequent entanglement of the secondary branches. These 

 exactly resemble the primary branch in size, length, and amount of 

 curvature, but appear to be invariably simple. 



1 See Geol. Mag. for July, p. 321. 



