THE AKENIG AND LLA.NDEILO EOCKS OE ST. DAVId's. 667 



Broadly nabelliform or semicircular ; branches very slender, nex- 

 uous, springing from a short flexuous main stem, which ter- 

 minates proximally in a slight dilatation probably representing 

 the hydrorhiza ; bifurcating frequently throughout their length, 

 diverging only slightly from each other and soon becoming 

 almost parallel. 



This species differs from all the other known species of its genus 

 in the extreme tenuity of its branches. It is of rather frequent 

 occurrence, associated with two of the species with which it occurs 

 in the Quebec GroUp {Callograptus JSalteri and Tetragraptus serra). 

 The branches are distinctly striated ; but the hydrothecae cannot be 

 distinguished in any specimens we have found. 



The species seems to be nearly allied to Dendrograptus flexuosus ; 

 and had it not been referred by Hall, from the evidence afforded by 

 the more perfectly preserved examples from the Quebec Group, to 

 the genus Callograptus, we should have considered it to be a some- 

 what anomalous species of Dendrograptus. 



Log. Middle Arenig, Whitesand Bay. 



Callogeapttjs Salteki, Hall. PI. XXXYI. fig. 10. 



1865. Callograptus Salteri, Hall, Grapt. Quebec Group, p. 135, 

 pi. xix. figs. 5-8. 



Narrowly nabelliform, attaining a length of about six inches, and a 

 width of from two to three ; branches numerous, undulating, 

 apparently springing directly from the hydrorhiza without the 

 intervention of any common stem ; bifurcating at somewhat 

 distant and irregular intervals, diverging very slightly and 

 becoming almost immediately parallel, closely arranged, the 

 space between them being less than their width ; occasionally 

 anastomosing. 



This species is of frequent occurrence, associated with the pre- 

 ceding, and has a considerable range. 



We have specimens more entire and much larger than those 

 figured by Prof. Hall (from two to three times the size), and 

 showing the hydrorhiza, from which the branches appear at once to 

 originate ; but none of our specimens are in such a perfect state of 

 preservation as those from the Quebec Group. The hydrothecae 

 cannot be distinctly made out; but the zig-zag direction of the 

 branches, caused by their alternate disposition, is plainly apparent. 



Loc. Middle Arenig, Whitesand Bay. 



Genus Dictyogeaptus, Hall. 

 Dictyonema, Hall, Pal. New York, vol. ii. 



When Professor Hall proposed the name Dictyonema he was 

 evidently unaware that it was an old-established name for a genus 

 of plants. As this name therefore cannot stand, we feel certain the 

 alteration here proposed will meet with his approval. 



