LOWER CAMBRIAN. 43 



the frond, while in those genera the multiplication of the branches is by regular 

 dichotomy or is four rayed as in Phyllograptus. 



Associated with these organisms are fragments of other organisms which have 

 all the appearance of undoubted plant remains (described as Fucoides flexuosa by 

 Emmons), and from the absence of characteristic graptolites in the shales it would 

 seem to warrant the conclusion that these radiate specimens are not of graptolitic 

 origin, but are referable to the sponges or possibly the marine algae. 



The name Dactyloidites bulbosus is proposed for these fossils. 



The material studied by Professor Hall, although abundant, was poorly 

 preserved. Only a dark stain remained on the slate, and of the original 

 form nothing but the radiate arrangement of the lobes. The carbonaceous 

 matter referred to is shown as a very thin coating in a few instances, but 

 usually it is a dark coloration on the smooth surface of the slate. When 

 subjected to a high degree of heat it is burned off and only a faint trace of 

 the impression is left on the slate, as a slightly darker, smooth spot. The 

 annelid trails and what may have been a simple form of alga often show 

 more of the carbonaceous matter than the impressions of the medusae. It is 

 probable that the mud contained more or less carbonaceous matter that was 

 segregated in the annelid burrows and trails. The animal matter in the 

 body of the medusae may have produced the trace now found on their 

 impressions. The presence of the dark, carbonaceous matter is well shown 

 in fig. 1 of PI. XXIV, fig. 2 of PI. XXV, figs. 1, 5, and 6 of PI. XXVII, 

 and fig. 5 of PI. XXVIII. 



The reference of this fossil to the marine algae, by Dr. Fitch, was the 

 most natural one to make in view of the form of the specimens and the 

 presence of some carbonaceous matter. Professor Hall considered that the 

 forms were referable to the sponges or, possibly, the marine algae. My first 

 tentative opinion was that they suggested the impression of the mouth and 

 gastric cavity of a species of medusa. 1 Subsequent study of the fossil 

 medusae of the Middle Cambrian led to the view that it was the body of a 

 discomedusan, flattened in the slate, and not the cast of the interior. The 

 reasons for this view are based on the direct comparison of a large series of 

 specimens from the slate quarries at Middle Granville and the Middle Cam- 

 brian forms from Alabama. Reference to this comparison is made in speak- 

 ing of the relations of Brooksella and Laotira to other fossil medusae (p. 8). 



■Tenth Ann. Eept. U. S. Geol. Survey, Part I, 1891, p. 606. 



