508 J. Hopkinson — On New British QraptoUtes. 



and again, beyond this, the virgula is prolonged for a considerable distance. In the 

 more entire, but younger form, the periderm is seen to be prolonged for about half an 

 inch, and no virgula is apparent. In the mature and perfect form, beyond the most 

 distal hydrothecEe, the periderm seems to have split in two ; one portion, of which only 

 about a third of an inch is seen, is slightly bent outwards, while the other portion is 

 continued in a nearly straight line for about an inch and a half. 



A full consideration of the various questions which these forms suggest must be re- 

 served for another occasion. 



I name this species after the Eev. Thomas Hincks, F.E.S., author of "A History 

 of the British Hydroid Zoophytes," to whom I am indebted for valuable information 

 on these recent representatives of the Graptolites. 



Loc. Llandeilo ;— Sowen Dod, and Wanlock Water, "Wanlockhead, Lanarkshire. 



Family, Monodipkionib^. 



1. Dicranograptns rectus, sp. nov. — PI. XII., Fig. 10. 



Polypary with a very short diprionidian stem, wider near the 

 axil than at the proximal end, and dividing acutely into two long 

 and almost perfectly straight monoprionidian branches, which di- 

 verge from each other at an angle of about 20 or 30 degrees. Hydro- 

 thecae from 25 to 30 to the inch, free for about half the width of the 

 polypary ; curvilinear in outline, and slightly incurved towards the 

 distal end. Apertures forming an angle of about 45 degrees with 

 the axis. 



The stem is provided, as in all the species of the genus, with a 

 radicle and two lateral spines, processes from the first formed thec^. 

 It vairies in length from 1-lOth to l-5th of an inch, its length not 

 increasing with the age of the individual, for specimens with branches 

 not more than an inch long seem to be more frequently provided 

 with stems of the full length than those in which the branches have 

 attained the length of three or more inches. The outer margins of 

 the branches are continued in a straight line to the proximal end of 

 the stem, the margins of which thus form the same angle with each 

 other as the branches. At the axil a breadth of 1-lOth of an inch is 

 sometimes attained. The branches vary from l-30th to l-20th of 

 an inch in breadth, and are usually perfectly straight, but some- 

 times curve slightly inwards towards their distal end. The hydro- 

 thecEe have the curvilinear form peculiar to this and the allied genus 

 Dicellograptus, with the usual pouch-like indentations within which 

 the apertures are situated. Their outer margin is slightly indented, 

 and in the stem, and for a short distance along the branches, within 

 this indentation there is a slight protuberance from which proceeds a 

 slender spine, directed outwards, or but slightly towards the distal 

 end of the polypary. In general form the hydrothecse seem to be 

 intermediate between those of D. NicJiolsoni and D. formosus (Hopk.) . 



This species differs from all the others of its genus in having an exceedingly short 

 stem in proportion to the length of its branches, and in its branches being but very 

 slightly, if at all, curved. 



From the numerous specimens of this and other species of Dicranograptns which I 

 have seen in the neighbourhood of Wanlockhead, I am convinced that, within certain 

 limits, the length of the stem furnishes a character of specific importance. D. 

 ramosus (Hall) may be thus distinguished when the branches are only just beginning 

 to bud, and D. Nicholsoni (Hopk.) may be determined by the characters shown by its 

 stem when but a single hydrotheca has been developed on each rudimentary branch. 



Loc. Llandeilo : — Laggen Gill, Leadhills, Lanarkshire. 



