RETIOLITES. 



345 



Retiolites (Gothograptus) spinosus (Wood). Plate XXXIV, figs. 16 a—c. 



1900. Retiolites spinosus, Wood, Quart. Journ. G-eol. Soc, vol. lvi, p. 485, pi. xxv, figs. 29 a and b, 

 and text-fig. 26 a and b. 



Figs. 226 a— d.— Retiolites (Gotho- 

 graptus) spinosus (Wood). 



"W 



w 



. fl 



Polypary small, not exceeding 2 cm. in length, and widening rapidly to a 

 maximum breadth of about 1*8 mm. (exclusive of apertural spines) which 

 is then maintained. Sicula small, "5 mm. in length. Thecae eleven to ten 

 in 10 mm. j free for greater portion of their length ; apertural margins 



undulate and provided with long curved 



spines. Clathria fairly well defined, reticula 



somewhat coarse and irregular. 



Description.- — The polypary has an initial breadth 



of about '9 mm. which increases fairly rapidly up 



to l - 8 mm., which width is then maintained, so that 



distally the margins are sub-parallel. 



What appears to be the sicula is occasionally 

 visible just within the base of the reticula and has 

 a membranous test. It has a length of '5 mm., and 

 a well-marked virgula proceeds from its apex in the 

 normal manner. This is seen to be continuous 

 throughout the polypary and is occasionally pro- 

 longed beyond its distal extremity. 



In specimens in which the reticula has dis- 

 appeared (Fig. 226 d), the clathria is well defined. 

 The ventral lattice, the limiting strands of which 

 are undulating, shows each alternate pair of cross- 

 bars to be connected by a median vertical fibre, the 

 interspaces between these apparently marking the 

 apertures of the thecae (compare Wiman). There 

 are indications of two septal strands, one straight 

 and the other zig-zag, but the parietal lattices are 

 not well differentiated. The fibration of the reti- 

 cula is irregular, showing comparatively wide meshes 

 of very fine filaments. 



The apertural spines of the thecae are paired, 

 but as a rule only one spine is visible. These spines 

 always remain quite free, they are nearly as long 

 as the width of the polypary, and typically curve 

 downward, as in Hallog. mucronatus var. uimucronaius. 



45 



c d 



a. Proximal end, showing sicula. Speci- 



men on same slab as PI. XXXIV, 

 fig. 16 b. 



b. Complete specimen, showing sicula 



and virgula, and paired apertural 

 spines. Figured, ' Quart. Journ. 

 Geol. Soc.,' vol. lvi, pi. xxv, fig. 

 29 b. Coll. Elles. 



c. Sub-scalariform view, showing ven- 



tral lattice. Enlargement of part 

 of PI. XXXIV, fig. 16 a. 



d. Specimen showing clathria. Vicarage 



Eoad.Builth; Lower Ludlow Shales. 

 Coll. Wood. 



