-jus 



BRITISH GRAPTOLITES. 



Fias. 184 a and b. • — Amplexograptus 



/n'/v i-c<i ruins, Lapw. 





Jfr 



V 



a. Proximal end, obverse aspect, show- 



ing part of sicula and origin of 

 th. I 1 . Figured Lapworth, Ann. 

 Mag. Nat. Hist. [5], vol. v, pi. v, 

 fig. 25 e. Dobb's Linn, Glenkiln 

 Shales. Coll. Lapworth. 



b. Proximal end, reverse aspect. Ibid. 



Figs. 184 c and d. — Amplexograptus 

 pcrexcavatus, Lapw. 





<; 



W. 



grows downward to its aperture, and thence slightly upward and outward, giving 

 off a spine at the mesial angle. Th. I 2 grows across the sicula almost horizontally 



before turning upward, and has a spine which, if 

 not mesial, is at least sub-apertural in position. 

 The virgella and spines are each about 1 mm. in 

 length. 



In the obverse aspect the thecae have the 

 characteristic appearance of those of a Climaco- 

 graptus, a striking feature being afforded by the 

 excavations, which are thickened round their edges, 

 as are also the edges of the apertures. The free edge 

 meets the impressed edge at a sharp angle, and 

 the free wall itself shows a tendency to overhang. 

 In the reverse aspect the thecae present an appear- 

 ance intermediate in character between those of Orthogfa/ptus and Glyptograptus, the 

 free edge of the theca being rounded and inclined and only a short portion of the 



impressed edge being left visible ; the apertural 

 margin is slightly concave and oblique. In this 

 aspect the overlap is conspicuous, the ventral wall 

 extending almost to the central line of the polypary, 

 so that the thecae overlap for fully one half their 

 length, and their distinctly alternate arrangement 

 is clearly brought out. 



Occasionally an intermediate view is presented, 

 having the appearance shown in PL XXXI, fig. 

 15 c, where the apertural margin is shown as 

 distinctly convex. 



In neither obverse nor reverse aspect is there 

 any trace of a septal suture. 



Affinities. — A. perexcaoatus is clearly allied to 

 the American species, Diplog. amplexicaulis, Hall, 

 and probably also to Gl/yptog. teretiusculus. From 67. teretiusculus it may, 

 however, be readily separated by the pronounced concavo-convex section of the 

 polypary, and the fact that in the obverse aspect the theca? approximate more 

 closely to the Climacograptus type. A. pcrexcavatus may be separated from 1). 

 amplexicaulis by its smaller size and greater relative width, and the characters of 

 the distal portions of the thecae. 



Horizon and, Localities. — Glenkiln Shales and Lower Hartfell Shales (zones 

 of (1) Nemag. gracilis, (2) Dicellog. jiattdosus, (3) Glimacog. Wilsoni). 



8. Scotland .- Glenkiln Burn ; Black Linn ; Craigmichan Scaurs ; Dobb's Linn ; 

 Berrybush Burn ; Leadhills. Wales : Llandrindod Wells ; Tiddyndicwm ; St. 



V 7 



c. Distal thecae, obverse aspect, showing 



deep and conspicuous excavations 

 like those in Climacograptus. En- 

 largement of part of PL XXXI, 

 fig. 15 a. 



d. Distal theca;, reverse aspect (part in 



relief, part as an impression), show- 

 ing Diplograptus appearance, Dobb's 

 Linn, Glenkiln Shales. Coll. Lap- 

 worth. 



