THE ABENIG AND LLANDE1L0 BOCKS OP ST. DAVID'S. 653 



We have only a single specimen of this species, probably of a 

 young individual ; for there is scarcely more than the funicle seen, 

 slight traces of hydrothecse being visible only at the extremities of 

 some of its subdivisions. The funicle branches most irregularly, 

 some of its divisions not bifurcating more than once, while others 

 give off branches repeatedly at distances of a quarter of an inch 

 or less from each other. It covers a space of about an inch 

 square. The branches ultimately given off are at least sixty in 

 number. 



From the Clonograptus (Qraptolitlius) multifasciatus of Hall, the 

 only other species of the genus known, G. implicatus differs in its 

 more slender, more nexuous, and more frequently branching funicle, 

 and in the greater number of branches to which it gives origin. 



hoc. Middle Arenig, Whitesand Bay. 



Family NEMAGRAPTID^E, Hopkinson. 

 Genus Nemageapttts, Emmons. 



Nemageaptus capillabis, Emmons. PI. XXXIV. figs. 2a & 2b. 

 Nemagraptus capillaris, Emmons, American Geology, vol. i. pi. i. 

 fig. 7. 



Principal branches compound, thread-like, and highly nexuous, 

 diverging in approximately opposite directions from a central 

 point, and giving off a few similar short and simple secondary 

 branches at subregular intervals, from one margin only ; sicula 

 and hydro thecae unknown. 



This is in many respects a most extraordinary form. The highly 

 flexuous, smooth, and excessively slender branches, offering no trace 

 of the marginal denticles so characteristic of the branching Rhabdo- 

 phora, compose a polypary whose general appearance is strikingly 

 distinct from that of any other known species of Graptolite. Our 

 examples, which lie in a tangled group of whitish threads imbedded 

 in a dark greenish grey matrix, admit of immediate identification 

 with Emmons's species (Amer. Geol. loc. cit. supra). Neither his 

 specimens nor our own offer anj^ conclusive evidence of the manner 

 in which the two main branches originate from the sicula. Judging 

 from the distribution of the branchlets, the only view which seems 

 probable is that the central branchlet is formed by the prolongation 

 of the minor extremity of the sicula, while the main branches both 

 originate immediately at its major extremity, as in the greater pro- 

 portion of the siculate Ehabdophora. In the two known forms 

 which most closely approach the present species in general appear- 

 ance, viz. Nemagrajotus (?) fragilis, Mch., sp., and Leptograptus 

 capillaris, Carr., sp., the main branches also originate from the 

 major end of the sicula ; and in the last-named species the minor 

 extremity frequently develops a central branch. If this be the 

 mode of growth in the present species, it differs most notably from 

 that which obtains among the species provisionally referred to 



