318 



^Ir. J. Hopkinson on a Specimen of 



pyrites is 



Fig. 1. 



the liydrotliecffi, and tlius have caused the ])olj]iary to be un- 

 evenly compressed. The most perfect are pear-shaped in form, 

 l-6th of an inch long, and at their narrow end, by which they 

 are attached, about l-30th of an inch wide. They have appa- 

 rently been bounded by a single marginal fibre, which is 

 slightly thickened at its edges, and, where the 

 removed, has impressed a fine 

 double groove on the siu'face of 

 the shale. If the fibres were 

 slender tubes, this appearance 

 would naturally be presented ; 

 for their outer margins would 

 offer the greatest resistance to 

 compression. The so-called 

 solid axis of the graptolite fre- 

 quently presents a similar ap- 

 pearance. At the proximal 

 end of the polypary these fibres 

 only are preserved, the oldest or 

 first-formed gonothecge having 

 fulfilled their function and pe- 

 rished. The distal extremity of 

 even the most perfect is not 

 clearly defined, the impression 

 of the capsule in most cases 

 becoming gradually less per- 

 ceptiljle from the proximal to 

 the distal end. Sometimes the 

 capsules are irregularly rup- 



Diplograpms itristis 



■with reproductive capsules. 

 Mayn. 3 diameters. 



tm-ed, their torn jagged edges 

 being distinctly seen, while one 

 has split along its marginal 

 limit, along the line of the marginal fibre, which appears to have 

 parted abruptly near the distal end of the capsule at one side, 

 and ^A\t acutely for some distance along the other side. This 

 would apjiear to indicate that the capsule may be composed of 

 two membranes joined together at their edges, through which 

 the fibre, if it l^e not merely a tube formed by a kind of double 

 marginal seam, has run. In no case can a distinct unruptured 

 distal orifice be traced. 



The gonothecffi present other peculiar appearances. To- 

 wards their jjroximal end they are sometimes longitudinally 

 corrugated or crumpled, or traversed by fibres Avhich extend 

 for some distance into the body of the polypary. Some are 

 much twisted and bent about, occasionally overlapping each 

 other. Between two which thus overlap, or perhaps only 



