662 J. HOPKINSON AND C. LAPWOETH ON THE GEAPTOLITES OP 



Ptilogeapttjs acutus, Hopk., sp. nov. PL XXXVII. figs. 

 la&lb. 



Slender, frequently branched, the branches simply pinnate, forming 

 only a small angle with each other, slightly waved and scarcely 

 thicker than the branchlets; branchlets or pinnae alternate, 

 flexuous, from half to three quarters of an inch in length, 

 diverging from the primary branches at a small angle (usually 

 30° to 40°) ; hydro thecae 18 to the inch, forming distinct, 

 distant, acutely pointed denticles with a slightly concave outer 

 margin; apertural angle acute. 



In its mode of branching this species somewhat resembles Ptilo- 

 graptus plumosus, Hall; but the branches bifurcate more acutely, 

 and are scarcely, if at all, thicker than the pinnae they support. 

 The hydrothecae are quite unlike those of any species of Ptilograjptus 

 yet figured. They so nearly resemble, however, those of Monograjptus 

 acutus, Hopk., that we have given to this unique form the same 

 specific name. 



This species is the only Ptilograptus known to occur in the Llan- 

 deilo formation. 



Log. Lower Llandeilo, Abereiddy Bay (lower zone). 



Family CALLOGHAPTID^E, Hopkinson. 

 Genus Dendeogeaptus, Hall. 

 Dendeogeaptus flexuosus, Hall. PL XXXVI. figs. 3a-3d. 



1865. Dendrograptus flexuosus, Hall, Grapt. Quebec Group, p. 127, 

 pi. xvii. figs. 1, 2. 



Broadly expanding, usually covering a space about an inch and a 

 half square ; branches slender, flexuous, springing from a short 

 robust common stem, bifurcating more or less regularly and 

 diverging equally, forming at first a considerable angle with 

 each other, but soon becoming nearly parallel, gradually less- 

 ening in width from their origin to their extremities ; hydro- 

 thecae about 30 to the inch. 



This species, which is pretty well represented in the St.-David's 

 beds, is at once recognized by its widely divergent form and slender 

 flexuous branches. 



One of the specimens figured shows, at its proximal end, a process 

 which may represent the hydrorhiza of the recent Thecaphora, the 

 main stem being here greatly widened out as if for attachment. 

 Branches are soon given off, the outer ones on each side bending 

 outwards with a curvature that brings round the numerous slender 

 branchlets to which they give origin, so that these two widely diver- 

 gent portions of the Graptolite are again brought together, the central 

 portion not being perceptible beyond the first or primary branches. 

 In this example (fig. 3 b) the branches diverge from each other at a 

 wider angle than usual ; and it may possibly prove to be a distinct 



