136 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 Reliograptus of Hall included three distinct genera. The title 

 of Retiograptus is best restricted to the forms to which it was first applied, viz., 

 those of the type Retiograptus tentaculatus, which combines the generic charac- 

 ters of Glossograpius and Lasiograptus . Clathrograptus embraces the simple 

 diprionidian forms of the type of Retiograptus Geinitzianus (Hall, non Bar- 

 rande). A third genus remains, which is typified by the extraordinary com- 

 pound species Retiograptus nucharis, from Lake St. John. 



Genus IX. Retiolites. Barrande. 



54. Sp 1. Retiolites fibratus. 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. 53°-) 



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 reti- 

 form covering. In addition to this network this form must have 

 possessed a continuous superficial membrane of sufficient thickness to 



