C. Lapworth — On Scottish 3Io7iog rapt idee. 317 



answer precisely to liis description, and, like his examples, generally 

 occur in matted groups. Compare Plate X. Fig. 10 c. 



Var. INVOLUTUS. Plate X. Fig. 11. 



GraptoUtes Nilssoni, Nicliolson ; Quart. Journ. Geol. See. 



vol. xxiv. plate xx. fig. 18. 



What seems to be a variety of this species is not uncommon in 



the highest zones of the Birkhill Shales. It is enrolled in an 



irregular spiral, and the earlier denticles frequently have their 



extremities recurved. 



Locality. — Typical form, Upper beds of the Birkhill Shales at 

 Dobbs Linn, Frenchland, Garple, Duffkinnel. 



7. MoNOGEAPTUs GREGARius, sp. nov. Plate X. Figs. 12 a — c. 

 Graptolithus Nilssoni, Barr. ; Grapt. de Boheme, pi. ii. fig. 17. 

 GraptoUtes Nilssoni, Harkness ; Quart. Journ. Geol. Soc. vol. 



vii. plate i. figs, 7 a — d. ISicholson, Quart. Journ. Geol. Soc. 

 vol. xxiv. plate xx. fig. 19. 



Polj^pary curved, short, rigid ; one to one and a half inches in 

 length, and with a maximum diameter of one-twentieth of an inch. 

 Hydrothecse arranged on the convex margin of the polypary, adnate 

 to the periderm, in contact only, triangular in form ; outer edge 

 concave, apertural edge straight, at right angles to axis of polypary, 

 denticle conspicuous. 



This is one of the best characterized species of the group. It has 

 hitherto been strangely confounded with Monogr. Nilssoni, with 

 which it has scarcely a character in common. The pol^'pary is, as a 

 rule, about one inch in length ; but sometimes examples are met 

 with which have an extent of 2J inches. These have a superficial 

 likeness to similarly sized examples of M. intermedins. From all 

 other species the size and shape of pol3q3ary at once distinguish it. 



The sicula in Monogr. gregarius may fairly be termed gigantic. It 

 often reaches a length of one-fourth of an inch before the primordial 

 theca is developed, and its broad extremity communicates a peculiarly 

 blunt appearance to the proximal end of the adult polypary. The 

 specimen figured (Plate X. Fig. 12c) is from the Skelgill Shales of 

 the Lake District, but the sicula is quite as conspicuous in Scotch 

 and Irish examples. 



Locality. — This species characterizes a distinct zone of the 

 Birkhill Shales, in which it swarms in extraordinary profusion at 

 Dobbs Linn, Frenchland, Garple, Dumbreddan, etc. 



8. MoNOGRAPTUs ATTENUATus, Hopkinson. Plate X. Figs. 9 a — d. 

 Graptolithus attenuatus, Hopkinson ; Geol. Mag. 1872, Vol. IX. 



Plate XII. Figs. 3 a—c. 

 The most slender species of the Monograpti yet discovered. Mr. 

 Hopkinson gives a very full and accurate diagnosis of it. He 

 believes, however, that its hydrothecaa are separated from each other 

 by a slight interval : and that it is in this respect allied to Rastrites. 

 Examples preserved with a portion of their relief prove, however, 

 that, as in all species of this type, the hydrothecEe are truly in contact. 



