168 BRITISH GRAPTOLITES. 



are in the well-known collection of Mrs. Gray of Edinburgh, and there are also a 

 few in that of Lap worth. 



Dicranograptus brevicaulis, sp. now Plate XXIV, figs. 3 a — d. 



1876. Dicranograptus formosus, Lapworth, Cat. West. Scott. Poss., pi. iii, fig. 75. 



Polypary consisting of a very short biserial portion 2 — 4 mm. in length, and 



two slightly curved uniserial stipes which may attain a length of 8 cm. or 



more ; axillary angle about 30°. Theca? short, twelve to ten in 10 mm., with 



free part of outer wall slightly curved ; apertures approximately horizontal, 



opening within ponch-shaped excavations which occupy one half to one third 



the width of the stipe. 



Description. — The biserial portion of D. brevicaulis is composed of 3 — 5 thecas 



on each side and widens throughout its extent from *8 mm. at the proximal end 



to 1*5 — 2 mm. at the axil. The uniserial stipes include between the dorsal walls 



an angle of 30° and are as a rule approximately straight 



Fig. 105. — Dicranograptus brcvi- . ' 



cauiis, sp. nov. for at least the first 4 cm. of their length ; subsequently, 



however, they curve inward so as to become almost 

 parallel to each other. In small specimens, owing to 

 the straight early growth, there is as a rule no indication 

 of this ultimate parallelism of the stipes. 



The sicula has not been observed, but its apertural 

 spine has been detected at the proximal end of the 

 polypary, and all the thecae of the biserial portion are 

 furnished with spinose outgrowths from their outer 

 walls. Spines are present only on the most proximal 



Biserial and uniserial portions in . 



partial relief, showing form of tnecse or the uniserial stipes and are often inconspicuous. 



thecaj. Enlargement of part rm ,-, , , , , ,. , -, _ 



of pi. xxiv, fig. 3 c. the tneca3 have an average length of about 1*5 mm. 



and overlap each other for about half their extent. In 



some aspects the thecce resemble those of Dicranog. rectus, but more usually they 



approximate closely to the Olimacograptus type, and 1). brevicaulis is therefore 



placed in the same group as D. tardiusculus. 



Affinities. — I), brevicaulis is very similar in form to all the short-stemmed 

 Dicranograpti. It differs from D. Clingani in the greater length of the 

 stipes and in the character of the thecas ; and from JJ. rectus in its shorter stem. 



Horizon and Localities: Llandeilo (Leptograptus Beds), Glenkiln Shales. 

 Shropshire: Spy Burn. Radnorshire: Castell, West of Builth. S.Scotland: 

 Glenkiln Burn ; Rein Gill ; Water of Deuch ; Stinchar Valley ; Birnock Water, etc. 

 Ireland : Ballygrot. 



