262 BRITISH GRAPTOLITES. 



change in the shape of the thecas in the different parts of the stipe, but also by 

 their greater number in a given unit of length. 



Horizon and Localities. — Llandeilo-Bala, Dicranograptus Shales. 



Shropshire : Oakwood, Pontesford. N. Wales : Conway Railway Cutting. 

 8. Wales : Taff Bridge, St. Clears; Railway S. of Bletherstone, etc. 



Associates, etc. — Mesog. multidens occurs in a fine state of preservation in 

 the Habberley Brook at the Oakwood. It also occurs in S. Wales, but the forms 

 are usually somewhat narrower than those from Shropshire, and, when cleaved, 

 bear at first sight a certain resemblance to Glimacog. tubuliferus. The species is 

 commonly associated with Dicellog. sextans, Dicranog. brevicaulis, Orthog. acutus, 

 and Amplexog. perexcavatus in the highest Glenkiln and Lowest Hartfell horizons. 



Collections. — Mr. Benson, Mr. B. Smith, Sedgwick Museum, Geological Survey 

 of England and Wales, Lapworth, and the Authors. 



Var. compactus, Lapworth. Plate XXXI, figs. 10 a — c. 



1873. Diplogra/ptus compactus, Lapworth, nom. nudum, Geol. Mag., vol. x, p. 134. 



What appears to be a distinct variety of Mesog. multidens occurs commonly at 

 a slightly higher horizon than the typical form, and was distinguished by 

 Lapworth in 1873 as Diplog. compactus, but not described or figured. It differs 



Pig. m.-Mesograptns multidens, var. fr0m 0UI * tyF * 1 form m tlle following particulars : 



compactus. (]) the polypary is narrower; (2) the thecas are 



I j smaller ; and (3) have less overlap. 



\ ' *f The polypary has a length of 5 — 6 cm., and an 



average breadth of rather less than 3 mm., which is 



i "i attained within 2 cm. of the proximal end where 



the width is about 1 mm. The apertural margins 



of the two basal thecas are conspicuously spinose ; 



Proximal end, reverse aspect. Enlarge- those of the more distal thecas are distinctly 



ment of part of PI. XXXI, fig. 10 c. J 



undulate, and closely resemble those of Orthog. 

 calcaratus. The overlap never exceeds one half. As in the typical form, the 

 polypary is furnished with a broad, flattened central tube, which probably contains 

 the virgula. 



Affinities. — In the characters of the distal thecse, var. compactus approaches 

 Orthog. calcaratus. It may, however, be distinguished from the forms belonging to 

 that species by its smaller breadth and the characters of the proximal thecas. 



Horizon and Localities. — Lower Hartfell Shales (zone of Dicranog. Olingani), 

 Dicranograptus Shales. 



8. Scotland : Dobb's Linn, etc. S. Wales .• ? Railway S. of Bletherstone. 



