43 



angles ; they are narrow in their origin, but expand abruptly and 

 attain their full width in a distance of three or four cellules. The 

 distal extremities of the stipes are also abruptly rounded. 



The genus Tetragraptus occurs only in the Skiddaw Slates in 

 Britain, and in Canadian rocks commonly regarded as of the same 

 age. 



The genus Dichograptus comprises forms consisting of eight or 

 more monoprionidian stipes united at the centre by a funicle, which 

 gives off two branches at each end, these are again subdivided. 

 Both the funicle and its subdivisions are generally, though not 

 always, enveloped in a thin corneous disc, or float, which often 

 extends a short distance along each stipe. The portion of the 

 stipes enclosed within the disc is always non-celluliferous. When 

 the disc is not present, the cellules usually commence on each 

 stipe, near the point of junction with its neighbour. 



Dichograptus octobrachiatus (Fig. 12) consists of forms having 

 eight monoprionidian stipes, united in the usual way, and a central 

 disc is present in most cases. Within the disc, or near it, the 

 stipes are about one-twentieth of an inch in width, in full grown 

 members ; beyond this the width, including the cellules, is about 

 one-eighth of an inch, and the common body occupies about one- 

 third of the entire width. The largest members of this species 

 measure as much as eighteen or twenty inches across, each stipe 

 being half that length ; and if they possessed in the central disc 

 the power to float or to sink at pleasure, as it is supposed, they 

 must have presented a very strange appearance on the surface of 

 the water. 



I have in my collection two species that have not been described 

 or named, and which for the present I will call No. i and No. 2. 

 No. I consists of four monoprionidian stipes, two of which spring 

 horizontally from a central point, curve slightly upward, and then 

 go off at an angle of eighty-five degrees. At the end of the curve, 

 each stipe throws off a branch on the inner side (Fig. 13). The 

 stipes are about an inch and a half in length, and one-twelfth of 

 an inch in width at the widest part, and are celluliferous on their 



