140 Dr. H. A. Nicholson on some Fossils 



them, as might be expected when we consider the number and 

 complexity of the Quebec Graptolites. It would seem, there- 

 fore, that the constant association of these fossils with Grapto- 

 lites (whenever these latter occur in any plenty), and their 

 constant absence from strata in which Graptolites are unknown, 

 constitute extremely strong proofs as to there being a natural 

 connexion between the two sets of organisms. 



Without entering further into their nature at present, I shall 

 simply describe three well-marked forms of these bodies which 

 occur in the shales of the Quebec group, and which differ both 

 from one another and from the forms which are found in the 

 Graptolitiferous rocks of the south of Scotland and the north 

 of England, 



Dawsonia acuminata, Nich. 

 Capsule of a long oval shape, having one extremity prolonged 

 gradually, and without any marked line of demarcation, into a 

 long acuminate mucro. The marginal fibre extremely delicate, 

 and not always to be detected. Often showing an impressed 

 line, which proceeds inwards from the mucro to a greater or 

 less distance within the sac. Dimensions variable ; in the 

 Quebec specimens mostly about one fifth of an inch in length 

 by one tenth of an inch at the greatest width ; in English spe- 

 cimens the average dimensions as above, but large examples 

 showing a length of two fifths of an inch by a greatest width 

 of three twentieths of an inch. (Fig. 3, a, a'.) 



Fig. 3. 



m ^'^P '^'^P ^^9 



Various forms of Dawsonia : a, Dawsonia acuminata, natural size ; a', the 

 same, enlarged ; b, D. rotunda, natural size ; b', the same, enlarged ; 

 c, D. tenuistriuta, natural size ; c', the same, enlarged ; d, d', another 

 variety of D. tenuistriata ; e, /, forms of D. camjmnulata, enlarged. 



Dawsonia acuminata is exceedingly abundant in some beds 

 of the Quebec group at Point Levis, where it constitutes the 

 commonest form of the genus. The species also occurs not 

 uncommonly in the anthracitic shales of the south of Scotland 

 (Upper Llandeilo). The size of the Quebec specimens is ex- 

 ceedingly uniform, whereas English specimens vary extraordi- 



