132 PEOCEEDIKGS OF THE GEOLOGICAL SOCIETY. 



Graptolites latus, M'Coy (in part) (Quart. Journ. Geol. Soc. 

 vol. iv.). 



This is by far the connnonest species of Tetragrapsus in the 

 Skiddaw Slates, and is certainly identical with the Canadian form. 

 All the specimens also of Didymograjpsus caduceus, Salt., which I 

 have seen from the Skiddaw Slates are likewise referable to this 

 species ; and it is further one of the commonest sources of the Grap- 

 tolites latus of M'Coy. The frond consists of four simple stipes, 

 which spring from a short central funicle, and are almost always 

 characteristically reflexed. The stipes are narrow at their origin, 

 but rapidly expand, some to a width of -l of an inch, again con- 

 tracting towards their distal extremities. The cellules are from 20 

 to 24 in the space of an inch, the denticles pointed, and the lower 

 margin of the cell-aperture strongly produced, and almost mucro- 

 nate, so as to render the outline of the cell-mouth curved. The four 

 stipes are seldom all visible at the same time in any single specimen, 

 one pair being almost always better exhibited than the other ; 

 but great variations in this respect exist in different individuals. 



Log. Barff, Outerside, Prozzengill. 



Genus Phtllogeapstjs, Hall. 



In this genus, according to Hall, the frond consists of " foliiform 

 stipes, which are celluliferous upon the two opposite sides, the margins 

 having a mucronate extension from each cellule." Phyllograpsus 

 differs from Diplograpsus in the fact that in the latter the frond 

 consists of two simple stipes united by their axes, whilst in the 

 former the frond is comprised of four such stipes united back to 

 back by their solid axes. It is possible, as conjectured by HaU, 

 that Pliyllograpsus was really doubly compound, many fronds being 

 united to one another at their proximal extremities ; but I have met 

 with no specimens which would countenance this view. It is some- 

 what curious that, of aU the genera which are exclusively confined 

 to the Skiddaw series, this is the only one which is known to occur 

 in the upper beds of the group. 



7. Phtllogeapsijs Ais^GUSTrpoLnrs, Hall. (Grapt. Quebec group, 

 p. 125, pi. 16. figs. 17-21.) 



In this species the fronds are " elongate -elliptical, or elongato- 

 lanceolate," the widest portion being a little above the base. The 

 ordinary length of the frond is 1| inch ; but I have found speci- 

 mens which reach a length of nearly 2 inches, being ^ of an inch 

 in excess of the longest observed by Hall. The cellules in my 

 specimens are about 30 in the space of an inch (according to Hall, 

 24), shghtly curved, wider at the aperture than internally, the 

 lower margin at the cell-mouth being prolonged into a strong tri- 

 angular mucro, which is usually somewhat deflexed. There are 

 indications of a central axis ; but these are not well marked. This 

 beautiful species is distributed throughout the entire Skiddaw series ; 



