DICRANOGRAPTUS. 1 69 



Asso&kites, etc. — V. brevicaulis is a fairly abundant form in the higher part of 

 the Glenkiln Shales of S. Scotland, where it occurs associated with Dicellog. sextans, 

 Nemag. gracilis, Dicranog. rectus, Dicranog. celticus, Diplog. angustifolius, Dialog. 

 Whitfieldi, etc. It is also met with in the Leptograptus (Glenkiln) Beds of Shrop- 

 shire associated with Dicranog. rectus, Dicellog. divaricatus, var. salopiensis, and 

 Nemag. gracilis. The best specimens known to us are in the collections of 

 I .a)) worth and the Geological Surveys of England and Scotland. 



Gnour III. — Type Dicranog. rectus. 



Dicranograpti in which the thecal have gently curved ventral walls and slightly 

 introverted and introtorted apertures. 



Dicranograptus rectus, Hopkinson. Plate XXIV, figs. 4 a — e. 



1849. Oraptolithus ramosus, Salter, Quart, Journ. Geol. Soc, vol. v, p. 16, pi. 1, fig. 7. 

 1872. Dicranograptus rectus, Hoplnnson, Geol. Mag., vol. ix, p. 508, pi. xii, fig. 10. 



Polypary consisting of a fairly long biserial portion G — 8 mm. in extent, and 

 two straight uniserial stipes G cm. or more in length ; these include an angle 

 of 20° — 30° between their dorsal walls, Avhile their ventral margins practic- 

 ally form a straight line with those of the biserial portion. Theca3 twelve 

 to ten in 10 mm., of the general Dicellograptus type, with free outer walls 

 gently curved, and slightly introverted apertures, which open within narrow 

 pouch-shaped excavations occupying about one third the width of the 

 stipe. 

 Description. — The biserial portion of the polypary is commonly made up of 

 about eight thecae on each side ; it is very narrow at its origin, measuring only 

 ■6 mm. j but at the point of divergence of the uniserial stipes the breadth is fully 

 2 mm. The uniserial stipes are long relatively to the biserial portion, frequently 

 attaining a length of 6 cm., and having a uniform width of 1 mm. They are 

 typically straight. 



Details regarding the proximal extremity are obscure, but there are indications 

 of the existence of a septum, although the thecal apertures on each side are 

 alternate. 



The theca? earliest formed are small, but throughout the biserial portion they 

 increase steadily in size, and ultimately in the uniserial stipes have a length of 2 

 mm. ; they overlap for one third to one half their length. There arc frequently 

 indications of spines on the thecae of the biserial portion, and also on the more 



