370 SCIENCE PROGRESS. 



graptus flabelliformis Eichw. which are so widely distributed. 

 This Dictyograptus, by the way. which has a very limited 

 vertical distribution, is probably in no way related to the 

 long-ranged Dictyonema. Graptolites are extremely rare 

 in the Upper Ludlow rocks, and have been detected in the 

 Lower Devonian rocks of Bohemia, though it is doubtful 

 whether their asserted occurrences in rocks of Devonian 

 age in Scotland and the Harz Mountains are correct. It 

 may be taken as fairly certain that they finally died out in 

 Devonian times. Between the earliest and latest graptolitic 

 deposits we have already a large number of graptolitic zones, 

 which it will be of use to print in one connected list as this 

 has not been heretofore done. So far as they have been 

 made out they are, in ascending order, as follows : Lingula 

 Flags ; (i.) Zone of Dichograptus? tenellus, Zone of Dictyo- 

 graptus flabelliformis. Tremadoc Slates; Zones of Bryo- 

 graptus. Areing Beds ; Zones of (i.) Dichograptus, (ii.) 

 Tetragraptus, (iii.) Didymograpttts indentus var nanus. 

 Llandeilo Beds; (i.) Zone of Didymograpttts Murchisoni, 

 (ii.) Zone of Ccenograpttis gracilis. Bala Beds; Zones of 

 (i.) Climacograptus Wilsoni, (ii.) Dicranograptus Clingani, 

 (iii.) Pleurograptus linearis, (iv.) Dicellograptus complana- 

 tus, (v.) Dicellograptus anceps. Llandovery Beds ; Zones of 

 (i.) Diplograptus acuminatus, (ii.) Diplograptus vesiculosus, 

 (iii.) Monograptus argenteus, (iv.) Monograptus convolutus, 

 (v.) Cephalograptus cometa, (vi.) Monograptus spinigerus, 

 (vii.) Rastrites maximus. Tarannon Beds ; Zones of (i.) 

 Monographts turriculatus, (ii.) Monograptus exiguus, (iii.) 

 Cyrtograptus Graycz. Wenlock Beds; Zones of various 

 species of Cyrtograptus not yet fully worked out. Lower 

 Ludlow Beds; Zones of (i.) Monograptus bohemicus, (ii.) 

 Monograptus Alilssoni, (iii.) Monograptus leintzvardinensis. 

 Upper Ludlozv and Lower Devonian ; Zones of undescribed 

 graptolites. 



It is quite certain that this number will be very largely 

 increased as a result of further work, but it is sufficient to 

 show the importance of the Lower Palaeozoic rocks when it 

 is remembered that many of these Zones contain a fauna 

 largely distinct from the faunas of the adjoining ones. 



