new Species of Oraptolites. 271 



2. Thamnograptus Doveri, Nieh. PI. VII. fig. 1. 



Polypaiy composed of a central undulating stem, about one 

 twelfth of an inch in width, giving off alternately placed 

 branchlets on the two sides. The branchlets are straight, 

 about one twenty-fourth of an inch in width, and placed at 

 intervals of from one quarter to half an inch apart (measuring 

 on the same side of the rachis). The terminations of the 

 branchlets are not shown ; but the longest ones preserved are 

 about an inch and a quarter in length, and show no sign of an 

 ending. No " solid axis " can be made out ; but portions of 

 the branchlets show very distinct transverse markings, which 

 have every appearance of being the mouths of cellules. 



Thamnograptus Doveri is readily distinguished from T. 

 typus, Hall, and T. Anna, Hall, by its much larger dimen- 

 sions and the remoteness and great length of the branchlets. 

 The only specimen known is a very well-preserved fragment 

 about two and a quarter inches in length, and exhibiting por- 

 tions of five branchlets on the one side and of six upon the 

 other. 



I have named the species in honour of Mr. W. K. Dover, 

 by whom it was discovered. 



Locality and Formation. — Randal Crag, Skiddaw. Lower 

 Skiddaw Slates. 



3. Didymograptus gibberulus, Nich. PL VII. figs. 3-3 b. 



Polypaiy bilateral, composed of two broad monoprionidian 

 stipes, which bend backwards from the sicula in gentle curves 

 at an angle of from 335° to 340°. The branches attain their 

 greatest width at their junction with one another and the 

 sicula, where they have a breadth of a line or more. The 

 two central cellules are vertical in position ; and from the ver- 

 tical line thus formed the cellules become more and more 

 obliquely divergent till they come to form an angle of about 

 45° with the back of the stipe. The cellules are about forty 

 in the space of one inch ; and their mouths, in well-preserved 

 examples, are furnished with very prominent mucronate tips. 



Didymograptus gibberulus belongs to the " reflexed " group 

 of the Didymograpti, and is very similar in general appear- 

 ance to the fossil described and figured by Mr. Salter under 

 the name of D. caduceus. The original specimen on which 

 this species was founded (Quart. Journ. Geol. Soc. vol. ix. 

 p. 87), however, is beyond doubt an example of Tetragraptus 

 bryo?ioides, Hall, or T. Bigsbyi, Hall, in which two of the 

 normal four stipes are concealed from view by the matrix. 



J 9* 



