132 
Lapworth— Graptolites of Co. Down. 
31. Sp. 2. Dimorphograptus elongatus. Lapw. PI. 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 coenosarcal 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 sinuatus. Nich. PI. 6, fig. 9. Locality— Coalpit 
Bay. 
36. Sp. 4. Diplograptus tricornis. Carr. PI. 6, fig. 10. Localities— Coalpit 
Bay, Ballygrot, and Craigavad. 
37. Sp. 5. Diplograptus angustifolius. Hall. PI. 6, fig. 11. Localities — 
Coalpit Bay and Ballygrot. 
38. Sp. 6. Diplograptus tamariscus. Nich. PI. 6, fig. 12. Locality— Coal- 
pit Bay. 
39. Sp. 7. Diplograptus dentatus. Brongn. PI. 6, fig. 13* Locality 
Ballygrot. 
