DICELLOGRAPTUS. 



161 



Var. rigens, Lap worth, MS. Plate XXIII, fig. 3. 



Fi«s. lul aand b. — Dicellograptuselegans 

 var rigens, nov. 



■^4 



a. Proximal end. Mt. Benger Burn, 



Hartfell Shales. Coll. Lapworth. 



b. Proximal thecae, showing introtor- 



sion. Ibid. 



At Mount Benger Burn, instead of the typical 

 l>. elegans, there occurs a variety which, while 

 agreeing with the typical form in the character 

 of the thecae, etc., differs from it in the almost 

 entire absence of curvature of the stipes. They 

 diverge continuously from their origin, and are 

 characteristically straight and rigid. 



So far as we are aware, this variety has only 

 been recognised at Mount Benger Burn, and its 

 horizon and associates are the same as those of the 

 typical form. The best specimens are in Lapworth's 

 collection. 



Dicellograptus caduceus, Lapworth. Plate XXIII, figs. 4 a — c. 



1876. Dicellograptus caduceus, Lapworth, Cat. West. Scott. Foss., pi. iv, fig. 83. 



1877. Dicellograptus caduceus, Lapworth, Grapt. Co. Down, p. 141, pi. vii, fig. 3. 



1902. Dicellograptus or Dicranograptus, T. S. Hall, Eec. Geol. Survey, N. S. Wales, vol. vi 

 pl.xiii fig.4. 



Pigs. 102 a and b. — Dicellograpt 

 ecus, Lapw. 



Stipes 6 cm. or less in length, typically crossing and twisting, to form a figure of 

 8, diverging at an angle of 340°, or rather less ; sicula rarely seen, but con- 

 spicuous when present; virgella and lateral spines clearly visible. Thecse 

 fourteen to twelve in 10 mm. ; ventral walls curved, overlapping one half to 



one third their length, which does not exceed 



1*5 mm. Apertures markedly introverted 



and introtorted ; excavation semicircular in 



form, and occupying one half to one third of 



the total width of the stipe. 



Description. — The stipes are "4 mm. wide at their 



origin, but increase to 1 mm. in their more distal 



portions. They are embedded more or less face 



downward upon the stone, so that their dorsal 



surface is turned towards the observer. Down the 



centre of this dorsal surface runs a longitudinal 



line, or sometimes two. Growth lines are generally 



very conspicuous; thus it would appear thai the 



jr 



b 



a. Thecse showing growth lines and two 



dorsal lines. Enlargement of part 

 of PI. XXI1T, fig. 4 a. 



b. Proximal end, showing sicula and 



mesial spines. Dobb's Linn, Hart- 

 fell Shales. Coll. Elles. 



