DIDYMOGRAPTUS. 17 



stipes of IK hlrundo and D. patidus often bear a very close resemblance to each 

 other, but those of I), hirimdo may attain a greater width. 



In the character of its proximal end D. hirimdo is closely connected with 1). 

 aparsas. It resembles this form in the unusually large size of the sicula and the 

 general proximity of the earliest developed thecEe ; it differs, however, in the 

 characters of the thecae in the distal parts of the stipes. 



Horizon and Localities. — Arenig, highest beds of Middle Skiddaw Slates (u})per 

 Tetragraptus beds) and base of Upper ISkiddaw Slates. Upper Mytton beds. 



Lalce District : Randal Crag, Skiddaw; Carlside Edge; Aik Beck; Outerside. 

 8. SJi,r()p,sJii re : Tankerville Road; W. of Stiper Stones. Lleyn Peninsula: Nant- 

 y-gadwen. 



Associates, etc. — D. hirundo occurs in abundance in the Lake district associated 

 with D. (jihherulus and Azijgograptns snecicns, in the Lleyn Peninsula, and also in 

 S. Shropshire, where it occurs to the exclusion of other species, forming a well- 

 defined zone in the upper Mytton beds. Numerous good specimens have been 

 found and are now in the collections of the Keswick Museum of Local Natural 

 History, British Museum, Geological Survey, and Woodvvardian Museum, Cam- 

 l)ridge, and in Lapworth's collection. 



Salter's type specimen (PI. I, fig. 5 c) is in the Museum of Practical Geology, 

 Jermyn Street. 



Didymograptus sparsus, Hopkinson. Plate I, figs. G a, h. 



1875. DidymograiAm sparsus, Hopkiusou, Quart. Jouru. Geo). Soc, vol. xxxi, p. 64.3, pi. xxxiii, 

 figs. 2 u, 2 d. 



Stipes 5 — 7 cm. in length ; fairly wide at origin, and increasing gradually to a 

 maxinnim of 3 nnn. ; diverging from a large sicula at a primary angle of 

 120°, but straightening at once and running horizontally. Thecge seven in 

 10 mm., inclined at about 45°, twice as long as wide, free one half their 

 length. A})ertural margins concave, approximately perpendicular. 

 Description. — The stipes measure 1*6 mm. in width at their origin, and gradually 

 v,^ 1A n-7 t ,„.,.o,,c TT^r^v,r,=r.,. wldcu u]j to a maximum of 3 mm. They are 



r IG. 10. — Dta!/»iO(;»'oj't!(s S2)arsMs, HopKinson. 1 J 



straight except in the region of the sicula, and 

 have been known to extend for 7*5 cm. on either 

 side of it. 



The sicula is large and conspicuous, it measures 



3'2 mm. in length ; the first theca originates near 



the apex, and grows down closely appressed to the 



^ZTl '^^^,Z:^^^^^^. Bicula throughout its length, reaching about 1 mm. 



Woodwardiau Museum. bcyoud it ; the crossiug Canal appears to be small 



and approximately horizontal in direction, so that theca 1^ arises at about the same 



level as theca 1', iuid grows down closely appressed to the sicula. This mode of 



3 



