DIPLOGRAPTUS. 239 



appears to be an indication of the presence of a partial septum in some of the 

 specimens. 



Affinities. — The small size of Orthog. cyperoides, and its relatively enormous 

 sicula, make it quite easy to recognise and distinguish it from all other Diplograpti 

 at present known. In the general characters of the polypary and the thecaj it 

 stands midway between the Orthograpti, on the one- hand, and the Petalograpti on 

 the other. 



Horizon and Localities. — Llandovery (Upper Birkhill Shales). Zones of 

 Monog. gregarius and M. con coin f us (including band with Cephalog. cometa). 



8. Scot hind: Dobb's Linn (Main Cliff and Long Linn) ; Belcraig. N. Wales: 

 Llanystwmdwy, near Criccieth. 



Associates, etc. — The Scottish specimens of 0. cyperoides agree very well with 

 the description given by Tornquist for his species, except that there appears to be 

 a trace of a septum in some specimens. Those from the zone of Monog. gregarius 

 are commonly associated with the zone fossil, M. triangularis and Gl. Tornquisti ; 

 while those from the higher zone of Monog. convolutus occur with M. convolutus, 

 Orthog. bellulus, and various Petalograpti. The Welsh specimens, collected by 

 Fearnsides, show some slight differences from the Swedish specimens, in that 

 the sicula is slightly shorter, and the polypary always appears to possess a partial 

 septum. These forms occur, too, at a somewhat lower horizon than those from 

 S. Scotland, being characteristically associated with Monog. fimbriatus. 



Collections. — Fearnsides and the Authors. 



Group III. 



Orthograpti in which the thecas were sub-rectangular in section and the 

 apertural margins strongly lobate ; excavation distinct. 



Diplograptus (Orthograptus) calcaratus, Lapworth. Plate XXX, tigs, la— c. 



1870. Diplograptus foliaceus, var. calcaratus, Lapworth, Cat. West. Scott. Foss., pi. i, fig. 30. 



Polypary robust, 8 to 10 cm. in length, wide at origin, attaining maximum 

 breadth of 2 - -5 to 3'5 mm. Virgular tube stout and prolonged. Virgella 

 conspicuous ; basal thecas adorned with long, stout spines. Theca) ten 

 to eight in 10 mm., 2*5 mm. in length, overlap not exceeding one half; 

 apertural margin strongly lobate, appearing rounded, concave, inclined, or 

 everted in the various views. 

 Description. — The polypary in Orthog. calcaratus often reaches a considerable 

 length; its maximum width, which varies from 2 - 5 to o - 5 mm. in different speci- 



