320 BRITISH GRAPTOLITES. 



that they appear to be naturally separable into four groups or sub-genera, 

 distinguished partly by the form of the thecse and partly by the nature of the 

 extraneous processes. 



Group I. — Lasiograpti in which the thecas approximate in form to those of 

 Glossograptus ; ventral spines and processes flexed, free or connected by a web ; 

 septal processes when present in the form of scopulae. 



=1 Hallograptus, Carruthers. 



Type Hallograptus mucronatus. 

 var. iuu tills. 

 var. bimucronatus. 

 sub-var. nobilis. 

 Group II. — Lasiograpti, in which the tbecas are of the typical Amplexograptvs 

 form ; ventral processes typically united to form a complete ventral lacinia. 

 = Thysanograptus nov. (Lasiograptus, Lapworth). 

 Type Thysanog. Harhnessi. 



var. costatus. 

 retusus. 

 Gi;oup III. — Lasiograpti in which the thecas resemble those of Hallograptus ; 

 ventral and septal processes united to form a peripheral lacinia. 



= Nymphogr aphis, Lapworth, MS. 

 Type Nyrnphog. velatus. 

 GitoiiP IV. — Lasiograpti in which the thecas appear to be of the type of 

 Hallograptus; polypary strongly clathriate ; ventral processes united to form 

 a ventral lacinia ; septal processes, when present, in the form of scopulse. 



— Neurograptus, Lapworth. 



Type Neurograptus fibratus. 



margaritatus. 



Sub-genus Hallograptus, Carruthers, MS. 

 1877. Hallograptus, Lapworth, Grapt. Co. Down, Proc. Belf. Nat. Field Club, p. 134. 



The name Hallograptus was originally suggested by Carruthers as the title 

 for a genus to include the forms Diplog. mucronatus and Diplog. bimucronatus. 

 The name was proposed in honour of Professor James Hall, who was the first 

 to figure the scopnlae or "reproductive sacs" which are commonly associated 

 with these forms, and was first published by Lapworth in 1877. 



We adopt this name as that of the first group or sub-genus of the Lasiograpti, 

 and include under it one species, two varieties, and one sub-variety. 



