/. Sopkinson — On New British Graptolites. 505 



polypary for about half an inch, and sometimes for a greater distance. 

 The hydrothecee have usually the appearance of rounded knobs, 

 their outer margins, forming a continuous curve, at first concave, 

 and then, for about half their length and round their apertures, 

 convex. 



This species somewhat resembles B. angustif alius (Hall), but is very much narrower, 

 and has hydrothecse more nearly approaching in form those of B. Mughetii (Nich). 

 As a rule, it is readily distinguishable, amongst the species with which it is associated, 

 by not having the same glistening appearance. It would seem to have had a thinner 

 or more fragile polypary than is usual in its genus. 



I name the species after Eobert Etheridge, Esq., F.R.S., Palaeontologist to the 

 Geological Survey of Great Britain, to whom I am indebted for the opportunity of 

 examining, at the Geological Museum, a collection of graptolites amongst which I 

 first recognized this form. 



Loc. Llandeilo : — Wanlock "Water, "Wanlockhead, Lanarkshire. 



2. Diplograptus penna, Hopk., Journ. Quekett Micros. Club, vol. i., 

 p. 159, pi. viii., fig. 12.— PL XII., Fig. 6. 



Polypary about 1-lOth of an inch broad, of unknown length, 

 and with the periderm and virgula distally prolonged. Hydrothecas 

 20 to the inch, never overlapping one another, their outer margin 

 convex, forming a^ angle of about 45 degrees with the axis, and 

 entirely free, and their distal margin, or margin of the aperture, con- 

 cave, and at right angles to the axis. 



From the proximal to the distal end the polypary gradually 

 widens, attaining its full width of 1-lOth of an inch at the last 

 developed hydrothecse. The entire polypary attains a length of at 

 least two inches ; but of the few specimens I have seen not one has 

 had both its extremities entire. The distal prolongation of a portion 

 of the polypary destitute of hydrothecee has only been seen in the 

 specimen figured. That this prolonged portion is the common tube 

 or periderm seems to be shown by the presence, throughout its entire 

 length, of a slender fibre, which, from its central position and dis- 

 tinct appearance, I have inferred to be the virgula. This periderm 

 appears, between one or two of the last-formed or most distal 

 hydrothec^, as a distinct structure — its junction with the thecee on 

 either side being well defined. It is here about l-lOth of an inch in 

 width, and shows transverse striae ; but as it leaves the thec^ these 

 markings disappear, and it contracts to nearly half this width. It 

 then gradually expands, attaining, at about two-thirds of its length,^ 

 a width of fully one-tenth of an inch, and gradually contracting to an 

 obtusely acuminate point. This free portion is about an inch and a 

 half in length. Whether the hydrothecEe have never been developed 

 along it, or after having budded from it have disappeared, or have 

 been destroyed during fossilization, we have no certain data to deter- 

 mine. From its varying width — its extensive dilatation and acuminate 

 apex more especially — the former supposition seems to be the most 

 probable. 



This curious structure is possibly morphologically identical with the "axial tube" 

 which, in B. vesiculosus (Nich.), is stated to take the place of the "ordinary solid 

 axis." In this species, however. Prof. Nicholson says that the presence or otherwise 



^ JSTear this point an accidental fracture is seen. It is represented in the figures. 



