THE AEENIG AND LEANDEILO ROCKS OF ST. EAVIe's. 643 



with the supporting periderm, is indicated in one or two instances 

 by a slight ridge. 



The maximum width of the branches observed in any specimen is 

 one fifteenth of an inch, and their greatest length 4 inches. 



Loc. Lower Arenig, Road TJchaf, Ramsey Island. 



Didymogeaptus sparsus, Hopk., sp. nov. PI. XXXIII. figs. 

 2a-2d. 



Brit. Assoc. Report, 1872. 



Branches linear, elongate, nearly as wide at their origin as at any 

 part of their length, diverging from each other at a primary 

 angle of about 240°, which by their curving soon becomes 180°; 

 sicula large, obtusely pointed; hydrothecae 15 or 16 to the inch, 

 inclined to the axis at an angle of about 45°, twice as long as 

 wide, and free for half their length ; apertural angle about 90°, 

 margin truncate. 



This species differs from nearly all the others of its genus, and 

 from all to which it is nearly allied, in the distance its thecae are 

 apart ; the width of the branches at their origin, which is one six- 

 teenth of an inch, is another characteristic ; whilst the unusually 

 large sicula, from which the branches proceed with a graceful curve, 

 forms such a conspicuous feature that it is usually alone sufficient 

 to indicate the species. 



The maximum width of the branches is one tenth of an inch ; the 

 geatest length observed, 3 inches. 



Loc. Lower Arenig, Road TJchaf, Ramsey Island. 



DlEYMOGEAPTTJS PENNATTJETTS, Hall, Sp. PI. XXXIII. figS. 3d-3e. 



1865. Graptolithus pennatulus, Hall, Grapt. Quebec Group, p. 82, 

 pi. iii. figs. 1-8, pi. v. fig. 9 (?). 



Branches narrow at their origin, more or less rapidly increasing in 

 width for about two thirds of their length, and then contracting 

 towards their extremities, diverging from each other at an angle 

 of about 180° or 200° ; hydrothecae from 25 to 30 to the inch, 

 long, narrow, and slightly curved outwards, inclined to the axis 

 at an average angle of from 40° to 60°, six (to eight) times as 

 long as wide, and with their outer margins free for about a 

 sixth of their length ; apertural angle from 100° to 120°, margin 

 concave ; denticles slightly mucronate. 



This species may be readily distinguished from all the others of 

 its genus by the narrowness of the branches at their origin and the 

 great width they ultimately attain. Measuring near their origin not 

 more than three or four hundredths of an inch, they frequentlty 

 attain a maximum width of three tenths of an inch. The resem- 

 blance between our specimens and Hall's figures is remarkably close. 

 From the species which are associated with the fragment he refers 



