us 



NE^y YORK STATE MUSEUM 



Fig-. 53 Tetragraptus 

 amii L., B. &W. Young- rhab- 

 (Uisome ; one branch missing-. 

 Keveise view. Shows point of 

 origin of first theca and direc- 

 tion of proximal portions of 

 branches. Deep kill. xi. 



lengtli 



Descrijjtion. Primary disk and nema not observed. Sicula incon- 

 spicuous, about 2 mm long. Brandies of first order (consisting of one theca) 

 narrow (.5 mm), 3.1mm long. Four branches of second order or main 

 stipes disposed horizontally, having a normal length of 30 cm, but attaining 



a maximal length of 60 mm and more ; those of either 

 side forming angles ranging between 70*^ and 90°, 

 widening within a few millimeters from the point of 

 bifurcation to the maximal Avidth (2.9 to 3 mm), 

 which is maintained to near the distal end. Thecae 

 slightly curved, numbering 9 to 10 in 10 mm, 

 about 3' mm long, inclined at 40" in their average, 

 of uniform width, three to four times as long as wide, 

 and overlapping about three fourths of their 

 Outer walls concave, apertural margin concave, normal to the axis 

 of the theca. 



Position and localities. Hall does not state the locality of the specimen 

 Avhich is referred by Elles and Wood to their ne^v species. At the Deep 

 kill we have observed this form only in graptolite bed 2 (Tetragraptus 

 zone), Avhere it is found associated with T. serra, T. fruticosus, 

 Phyllograptus ilicifolius, Didymograptus extensus, 

 etc. The authors of the species record it from 

 the Middle SkiddaAv slates, in association with 

 some of the species just mentioned ; and from 

 south Wales. 



Remarks. Elles and Wood state in their 

 work that this form was included by Hall (with 



doubt) in T. br}()Uoides ( = serra), and that Lapworth long con- 

 sidered it as distinct. Also, the present writer had recognized the differences 

 between this form and T. serra, when the description of the species was 

 published. While the dimensions and characters of the branches and thecae 

 are the same as in T . serra, the branches are here disposed horizontally, 

 instead of being reclined as in that form. This difference is most strikingly 



Fig. 54 Tetragraptus amii L., 

 E. & W. Fragment of branch. Deep 

 kill. x3.3 



