28 Proceedings of the Royal Society of Victoria. 



strongly striated and often deeply indented ; inner surface 

 celluliferous or serrate, as in Graptolithus." Although Professor 

 Hall indicates the occurrence of hydrothecse in the above descrip- 

 tion, it does not seem to me absolutely clear whether the whole 

 frond bears hydrothecpe or only a portion of it. Judging from 

 the specific descriptions, specimens with the hydrothecae preserved 

 must have been very rare indeed, as the majority of the species 

 which have come under my notice have been incomplete in this 

 respect. 



Zittel* gives the following definition: — " Hydrosome, funnel 

 pannier or fan-shaped, with numerous branches almost parallel, 

 strong, forked and united by cross-threads. The ends of the 

 branches are free, and are then set on one side with pointed 

 hydrothecse. The latter appear very perishable, and are exceed- 

 ingly seldom preserved." In this definition it is apparently 

 intended to indicate that only the free ends of the branches bear 

 hydrothecfe. In the specimen now before me the hydrothecaj 

 occur not only on the free ends of the branches, but are also 

 plainly seen on other parts of the frond, and I have been able to 

 trace them almost to the very centre of the polyp-stock. 



Mr. T. S. Hall remarks in connection with the description of 

 his species,! that "the diameter of a perfect specimen has not 

 yet been determined, and the hydrothecae are not visible in any 

 of the specimens." I will therefore avail myself of this opportu- 

 nity to add the following observations to complete the diagnosis 

 of— 



DiCTYONEMA GRANDE, T. S. Hall. 



The branches where the hydrothecse are well-developed are 

 from 2-5 mm. to 3 mm. broad. Hydrothecse long, narrow, 

 mucronate, indent the branches for about one-third the width 

 free for about one-fifth their length ; length 5 mm., breadth of 

 aperture 1 mm., but gradually narrowing towards the back of 

 the branch. The upper taiargin or aperture is decidedly concave; 

 the lower margin is straight, can be traced to a point opposite 

 the aperture of the third lower hydrotheca, and makes an angle 

 of about 15° with the back of the branch; the mucronate point 

 is set at about twice that angle, which gives a somewhat arched 



» Handb. d. Pal., Band I., p. 2S9. 



t Proc. Roy. Soc. Viet., vol. iv., N.S., pt. I., p. 8. 



