410 



MISS G. L. ELLES ON THE WENXOCK 



[May 1900, 



Fig. 23.— Cyr- 



tograptus rigi- 

 dus. 



a — proximal 

 type of cell, XO. 



b = type of cell 

 of branch (in re- 

 lief), X 5. 



Pi g . 24. — Cyr- 

 tograptus Lund- 

 greni. 



/T> 



a = proximal 

 type of cell, x 5. 



b — type of cell 

 of branch, X 5. 



[For comparison 

 with C. rigidus.] 



figures also show this latter 

 inclination (op. cii. pi. iv, 

 figs. 12 & 14). 



1 append a brief description 

 of the proximal part of the 

 rhabdosoma, as supplementary 

 to the description which Tullberg 

 lias already given : — 



Sicula very small and in- 

 conspicuous ; rhabdosoma very- 

 narrow at the origin, gradually 

 increasing in width up to the 

 point of origin of the only branch. 

 Proximal thecse triangular, with 

 slightly reflexed apertures^ in 

 contact only, numbering twenty- 

 four to the inch (nearly ten in 

 10 mm.). There are eighteen 

 theca? of proximal type, but only 

 thirteen before the branch is 

 given off. 



The proximal end is straight ; 

 it is never enrolled. 



Localities. — Dulas Brook; 

 River Irfon ; Sale. 



Cyrtogeaftus symmetricuSj sp. nov. (PI. XXIV, figs. 4 a 

 & 4 B.) 



Rhabdosoma unilateral, monoprionidian, with a slender proximal 

 part, but the distal part often attains a width of fully -fa inch 

 (1*5S7 mm.). One branch only is present, and its curvature is 

 similar in amount, but opposite in direction, to that of the main 

 stipe. The curvature of both lateral and main stipes is slight, but 

 elegant. 



The first theca arises from the base of a small sicula -Jj inch 

 (1-05 mm.) in length. The first eight cells are similar in character : 

 they are fairly large and triangular, with reflexed apices ; the 

 thecae are in contact only, and number twenty-four to the inch 

 (nearly ten in 10 mm.). 



The branch originates with the fifth or sixth theca, and the sub- 

 sequent change iu the character of the cells is very abrupt. 



After the eighth theca the thecse are tubular, with reflexed apices 

 furnished with distinct denticles. The thecae overlap one third of 

 their length, and are inclined at an angle of 20° to 25 3 ; the apertural 

 angle is about 130°, and the cells number twenty-six to twenty- 

 eight in the space of an inch (eleven in 10 mm.). The thecae are 

 seen to be situated on the concave side of the main stipe, which, 

 immediately after the branch is given off, quickly widens to T 1 ^ inch 

 (1*587 mm.). The branch is the exact counterpart of the distal 

 portion of the main stipe, differing only in direction of growth. 



