FAUNA OP THE ST. JOHN GEOUP. 35 



'■Correction. — When this p;iper had already been printed Prof. Brogger told me that he did not 

 share my views on the structure of Dktyonema flahelUforme, and ho considered that it reall}' has its 

 branches arranged in a funnel or inverted cone, and that it is endowed with hydrothec;e resembling 

 those of other graptolites. * * * Having heard Pi'of Brogger's opinion, I found in the museum of 

 the Swedish Geological Survey some well-preserved specimens in demi-relief, and I examined them as 

 accurately as possible. In splitting the plate I found that a lower lamina of the branching hj'dro- 

 some really originated from the same sicula as the upper lamina. On the lateral branches real hydro- 

 thecœ were apparent, resembling those of the Dichograplidse. That they arc so rarely observed 

 depends probably on the circumstance that thej' are directed inward toward the centre, and that they 

 are covered by the polyf)ary when compressed in the slate. On the lateral branches they are some- 

 times visible, because they are sometimes directed outward." 



This view of the form of the hydrosome of Dictyonema was stated by the late 

 Mr. Salter iu volume iii ' Memoirs of the G-eological Survey of Great Britain,' and is also 

 set forth by Prof. Hall in his original description of the genus. 



TuUberg's former view that the hydrosome was fan-shaped is that which at first sug- 

 gests itself, when we observe how invariably the iDolyparies are flattened out in the shale 

 in which they have been preserved. Dictyouema, as it floated in the ocean, was no 

 doubt fully expanded to a funnel or vasiform shape ; but while the delicate threads 

 w"hich maintained the hydrosome iu this shape were sufficient to keep the branches apart 

 in life, when in time it sank to the muddy bottom of the sea it collapsed, and the flattened 

 sides, being kept slightly apart only by the multitude of little spines of the hydrothecsc, 

 would nearly come together. Supported thus, a small space was left between the opposite 

 sides of the hydrosome, which gradually filled with fine mud ; when the shale is split away 

 from the hydrosome the spines of the hydrothecse of the lower side of the hydrosome are 

 sometimes seen as minute shining dots in rows betw^een the branches of the upper side of 

 the hydrosome. Owing to the irregularity of the inner surface of the hydrosome, the fos- 

 sil invariably splits along the .smooth outer surface, and thus the cells are usually invisible. 



Didyonemu flabellifoime is known from other countries than Scandinavia, Russia and 

 Britain. It has long been known to occur near Spa, iu Belgium, where it was at first 

 thought to be of vegetable origin,' and so considered until 184t. Prof C. Malaise ■ has 

 written an article on this fossil, which appears to be common at scA^eral localities in the 

 east of Belgium, and which there, as in most countries, is a solitary fossil in the sense 

 that few or no other species occur with it. Excepting two fucoids, the only fossil 

 announced is a lingula ; and in "Wales, according to Prof. Ramsay, only some small liu- 

 gulas occur with Dictyonema. The fauna described in the following pages is therefore 

 exceptionally rich for this horizon. 



Prof G-. Dewalque asserts that the geological position of this species is in the lower 

 part of the " système salmien " of And. Dumont, above the " système revinien," and that 

 it gives as definite a horizon in Belgium as it does in Wales and Scandinavia. Prof 

 Malaise considers that of the few Cambrian fossils found in Belgium Dictyonevtn sociale 

 {=^flabeUiforme) characterizes the Upper and Oldhamia radiata the Low^er Cambrian rocks of 

 that country. 



In two other districts of Eastern Canada beside that of St. John, Dictyonema fiabelliforme 



' Omalius d'Halloy, " Description géologique des Pays-Bas," 1828. 



2 " Documents palœontologiques relatif au Terrain Cambrien de l'Ardenne." Brussels, 1881. 



