DENDROID GRAPTOLITES OP HAMILTON, ONTARIO. 



29 



As the connecting filaments are very fine, owing to imperfect preservation, 

 they are not always distinct over the whole surface of the frond. Tliis si)ecies 

 is easily distinguished from D. gracilis — even in fragments — by the branches 

 being exceedingly fine (about one-hundredth of an inch in width), with scarcely 

 that distance between them, and witli no approach to the dendritic form of that 

 species. The frond maintains its character even in the young state. The larg- 

 est frond is three and one-half inches in diameter. 



It occurs in the Niagara limestone [dolomltic limestones of the cherty beds 

 and in the underlying more shaly rocks; 1884] at Hamilton, Ontario. The speci- 

 men described was obtained by Lieuteuant-Colonel Grant, and presented to the 

 writer. 



Spencer's description of 1884 adds, that the dissepiments are very 

 delicate, and the margin entire. He further says: 



This species is easily distinguished from D. gracile [ = D. crassihasale Gurley] 

 by the branches being much finer, less diverging, and with more bifurcations, 

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



Figs. 32, 33. — Dictyonema tenellum Spencer. 32, A small example peeserving the 



BASAL PORTION. (BY R. S. BASSLER.) 33, A LARGER RHABDOSOME. 



regularly circulai-, with no general bush-lilce form like that seen in most 

 specimens of D. gracile [crassibasalc]. The largest frond is 9 cm. in diameter. 



Gurley 's descrij^tion of the species is as follows: 



Polypary cyathiform, in the flattened state radiating from a center ; proximal 

 extremity only indistinctly visible in one specimen (text fig. 32). appearing to 

 consist of some kind of a bulbous or fibrous root. Branches straight, mostly 

 0.3-0.35 mm. wide; a few as narrow as 0.25; occasionally one as wide as and 

 none wider than 0.4 mm. Number of branches transversely in 25 mm., proxi- 

 mally about 45, distally 50-55. Interspaces consequently rarely as wide as and 

 usually much narrower than branches. Minimal length of meshes about 0.5 

 mm., maximum about 1 mm. Thecte invisible. Dissepimenta of about medium 

 thickness, straight or oblique. 



The identification of this species I consider thoroughly made out. There is no 

 other species at Hamilton, at least in my experience, to which Spencer's orig- 

 inal description could refer. But in 1884 Spencer figured as D. tenellum a 



