490 MISS G. L. ELLES ON THE GEAPTOLITE [^Ug. 1 898, 



in the Tetracjraptus pliyllograptoides of Swedish authors, in which 

 the stipes are united for some little distance at their proximal ends, 

 but are free above. 



{g) Tetkagraptus serea (Brongn.). 



1828. Fucoides serra, Brongniart, ' Hist. Veget. Foss.' vol. i, p. 71, pi. vi, figs. 7 & 8. 



1858. Graptolithus hryonoides. Hall, Geol. Surv. Canada Eep. 1857, p. 126. 



1863. Tetragrapsus \Jbryonoides], Salt. Quart. Journ. Geol. Soc. vol. xix,p. 137, fig. 8. 



1865. Gh'aptoUthus hryonoides, Hall, ' Grapt. of the Quebec Group,' Geol. Surv. 

 Canada, dec. 2, p. 84 & pi. iv, figs. 1-11. 



1868. Tetragrapsus hryonoides, Xicli. Quart. Journ. Geol. Soc. vol. xxiv, p. 131. 



1875. Tetragraptus serra, Hopk. & Lapw. ihid. vol. xxxi, p. 650 & pi. xxxiii, 

 fig. 10. 



There seems little doubt that Brongniart's Fucoides serra is the 

 same species that Hall described later as Graptolithus hryonoides; 

 in fact, Hall himself acknowledges this (' Grapt. of Quebec Group/ 

 p. 84), aud therefore the older specific name should be retained. 



The rhabdosoma presents great variation in form, owing to the 

 diff'erent ways in which it has been preserved. Sometimes the stipes 

 are spread out as in T. quadribrachiattis, at others they are directed 

 obliquely upwards. The two stipes of the 1st order (so-called 

 ' funicle') reach together a length of about -yJ^ inch (2*1 mm.). The 

 stipes resulting from the dichotomous division of these attain some- 

 times an enormous length, one specimen in the Woodwardian 

 Museum being about 9 inches (22*8 cm.) loug, and another rather 

 more than 7 inches (17'7 cm.) : the commoner forms, however, do 

 not exceed 2 inches (51 mm.) in length. These stipes are narrow 

 at their origin, but widen rapidly, and are found to have attained 

 their maximum width after the 3rd or 4th theca ; they become 

 narrower again at the extreme distal end, owing to the shortness of 

 the thecae at that point. The dorsal walls of the stipes may be straight 

 or curved. The width is very different in different individuals ; in 

 some, the width at the origin of the stipes is -gL inch (1*05 mm.), 

 and the maximum width attained -^^ inch (2*1 mm.), but in the 

 largest individuals the maximum width is fully ^- inch (4*2 mm,). 



The thecae vary in number according to the place of measure- 

 ment, size, and age of an individual ; near the proximal end 

 they may be twenty-six or even twenty-eight to the inch (ten to 

 eleven in 10 mm.), but in the adult part of the rhabdosoma the 

 number rarely exceeds twenty (eight in 10 mm.). The thecae are long, 

 somewhat curved, and are widest at their apertures ; their length is 

 about 3 times as great as their maximum width; they are inclined 

 40° to 50° (average 45°), and are free for about a quarter of their 

 length. Their apertures are concave and circular, and are inclined 

 to the general direction of the stipe at an angle of 110° to 120°. 



The sicula is fairly large and conspicuous in some specimens ; it 

 measures ^ inch (2-1 mm.). 



The species may be distinguished from Tetragraptus quadribra- 

 chiatus (Hall) by (1) the very rapid widening of the stipes and (2) 

 the greater width attained; and from T. Bigshyi by (1) fewer cells 

 in a given unit of length ; (2) general form and greater size when 

 mature. 



