136 



Dr. H. A. Nicholson on some Fossils 



evident on a comparison of the descriptions of the two forms, 

 seem to be quite constant, and appear to me to be quite sufficient 

 to establish the specific distinctness oi I), grandis. 



From D. quadrangularis, Hall [op. cit. supra, p. 138, pi. xx. 

 fig. 5), to which it also bears some resemblance, though not so 

 close a one, D. grandis is readily distinguished by the fact that 

 the branches of the former are nearly parallel and rarely bi- 

 furcate, whilst the fenestrules are very nearly square. 



Loc. and Form. Common in a single stratum of greenish- 

 grey shale, Point L^vis, the fronds covering large surfaces of 

 the beds. 



Tetragrapsus approximatus^ Nich. 



Frond consisting of four simple undivided stipes, arranged 

 bilaterally, two proceeding from each extremity of the funicle. 

 E-egarding the funicle as horizontal, the stipes are as nearly 

 as possible at right angles to it ; so that the two stipes on either 

 side of the funicle form nearly a straight line. Stipes curved 

 at their origin from the funicle, and then running nearly straight 

 and parallel to one another. The entire frond closely resembles 

 two examples of Didymograpsus ( Graptolithus) patidus^ Hall, 

 united back to back by their radicles (fig. 2, a). 



Fig. 2. 



Tetragrapsus approximatus, Nich. : a, a specimen nearly perfect, natural 

 size ; b, fragment of one of the stipes, magnified, to show the form of 

 the cellules. 



Dimensions of the frond in the largest specimen observed : 

 length of funicle one tenth of an inch ; width of funicle one 



