^76 TKANS. ST. LOUIS ACAD. SCIENCE. 



specimen is eight centimetres high and about sixteen broad, rising 

 from a united base of five or six stipes. 



Formation a?id Locality. — Niagara limestones at Hamilton, 

 Ontario. 



DiCTYONEMA WEBSTERI (DawSOn). 



(Acadian Geology, 1S6S.) 



This beautiful frond occurs at New Canaan, Nova Scotia, in 

 fawn-colored slate of the Upper Silurian system. It is cellulifer- 

 ous on one side, and in appearance it is more closely related to 

 D. retiforme than to D. gracile. 



DiCTYONEMA TENELLUM, nOV. Sp. 



Plate 1. Fig. 13. 



Dictyonema tenellum (Spencer). Can. Nat., vol. viii., No. S. i87«. 



Frond cyathiform in the growing state, but usually circular on 

 the rock. The branches uniform, diverging slowly from the radi- 

 cle-centre to the margin with bifurcations ; in width averaging 

 0.3 millimeters, and connected at short intervals by very delicate 

 transverse dissepiments ; margin entire. The frond is of a corne- 

 ous character like the other species of this group. 



In the best specimens distinct ellipsoid pits are arranged along 

 the sides of the branches, marking the position of the calycles, 

 these having the longer diameter equal to half a millimetre and 

 their shorter occupying two-thirds of the width of the stipe. 

 There are about twenty-four of these calycles arranged longitu- 

 dinally in the length of a centimetre. In specimens less perfectly 

 preserved the bars connecting the branches are almost obliterated, 

 and in those in a better state of preservation they are placed fiom 

 two to three millimetres apart, while between the branches there 

 are not usually spaces as great as (or greater than) their own 

 width. 



This species is easily distinguished from D. gracile by the 

 branches being much finer, less diverging, with more bifurca- 

 tions, by the transverse bars being more closely arranged and the 

 frond regularly circular, having no general bush-like form that is 

 seen in most specimens of that species. The largest frond is nine 

 centimetres in diameter. 



Formation and Locality. — It occurs at Hamilton, Ontario, in the 

 dolomitic limestone of the cherty beds and in the underlying more 

 shaly rocks. It was first collected by Col. Grant, 



