132 Lapworth— Graptoliies of Co. Down. 



31. Sp. 2. Dimorphograptus elongatus. Lapw. PL 6, fig. 6. Locality- 

 Coalpit Bay. 



Genus IV. Cephalograptus. Hopkinson. (Journal Quekett Micros. Club, 

 1869.) 



32. Sp. 1. Cephalograptus cometa. Geinitz. PI. 6, fig. 4. Locality —Coal- 

 pit Bay. 



Genus V. Diplograptus. M'Coy. (Annals and Mag. Nat. His.). 



In addition to the diprionidian form of the polypary, the chief charac- 

 teristic of this genus is generally held to be the fact that the central canal is 

 divided longitudinally, by a vertical septum or diaphragm, into two distinct por- 

 tions which do not communicate with each other — at least in the later stages 

 of the growth of the polypary. In one group, however — viz., the sub-genus 

 Glyptograptus (Lapw.)— none of the examples preserved with their relief which 

 have hitherto come under my notice, give evidence of the presence of this dia- 

 phragm; but, on the other hand, the ccenosarcal tube appears to be undivided, 

 and to be in organic connection with both series of hydrothecae, as in Retiolites. 



33. Sp. 1. Diplograptus acuminatus. Nich. PI. 6, fig. 7. 



The characteristic fossil of the lowest zone of the Llandoveries of South 

 Scotland. It is as yet unknown in Ireland. 



34. Sp. 2. Diplograptus modestus. Lapw. PI. 6, fig. 8. (Catl. Western 



Scott. Fossils. Plate 2, fig. 33.) Locality— Coalpit Bay. 



35. Sp. 3. Diplograptus smuatus. Nich. PI. 6, fig. 9. Locality — Coalpit 



Bay. 



36. Sp. 4. Diplograptus tricomis. Carr. PI. 6, fig. 10. Localities— Coalpit 



Bay, Ballygrot, and Craigavad. 



37. Sp. 5. Diplograptus angustifolius. Hall. PI. 6, fig. II. Localities — 



Coalpit Bay and Ballygrot. 



38. Sp. 6. DiplograpUis tamariscus. Nich. PI. 6, fig. 12. Locality— Coal- 



pit Bay. 



39. Sp. 7. Diplograptus dentatus. Brongn. PI. 6, fig. 13. Locality — 



Ballygrot. 



