36 
Lapworth— Graptolites of Co. Down. 
preserved specimens this skeleton is covered and partially hidden from sight by 
a thin continuous membrane showing cell-apertures. Locality— Ballygrot. 
The genus Reiiograptus of Hall included three distinct genera. The title 
of Reiiograptus is best restricted to the forms to which it was first applied, viz., 
those of the type Reiiograptus tentaculatus , which combines the generic charac- 
ters of Glossograptus and Lasiograptus. Clathrograptus embraces the simple 
diprionidian forms of the type of Reiiograptus Geinitzianus (Hall, non Bar- 
rande). A third genus remains, which is typified by the extraordinary com- 
pound species Reiiograptus nucharis , from Lake St. John. 
Genus IX. Retiolites. Barrande. 
54. Sp 1. Retiolites jibratus. Lapw. PI. 6, fig. 28. 
Polypary simple, diprionidian, one or two inches in length and one-fourth 
of an inch in breadth; margins parallel, proximal end broadly rounded 
and destitute of ornament. Virgula stout, straight, distally prolonged, 
Hydrothecae 24 to 28 to the inch, their position being indicated by 
broad regularly quadrangular meshes. Epiderm continuous, supported 
on a skeleton framework of interlacing threads. 
This form, which is remarkably abundant in the higher zones of the Lower 
Hartfell of South Scotland, is intimately allied to the forms here united under 
Retiolites perlatus (Nich. ), but differs from them mainly in the form of the thecal 
meshes, and in the frequent presence of lateral appendages. Locality— Carnalea. 
55. Sp. 2. Retiolites perlatus ? Nich. (Geo. Journal, vol. xxiv.. p. 530.) 
The original example of this species is too imperfectly preserved to enable 
us to recognize any specific character beyond the great breadth of the polypary 
and the extraordinary width of the dermal meshes. In this respect it agrees with 
certain views of the two following forms which occur in the South of Scotland, 
but neither of which it is as yet possible to identify with the R. perlatus of the 
Coniston Mudstones. 
56. Var. Daironi. Var. nov. Lapw. PI. 6, fig. 30. 
Occasionally three or four inches in length. In the characteristic view it 
resembles a gigantic specimen of Dip. palmeus (Barr.), with a ret.- 
form covering. In addition to this network this form must have 
possessed a continuous superficial membrane of sufficient thickness to 
