LASIOGRAPTUS. 



327 



Var. costatus (Lapworth). Plate XXXIV, figs. 2 a — d. 



1873. Lasiograptus costatus, Lapwortli, G-eol. Mag., vol. x, p. 559. 



1877. Lasiograptus costatus, Lapworth, Grapt. Co. Down, Proc. Belfast Nut. Field Club, p. 135, pi. 

 vi, fig, 26. 



In this variety the polypary is larger than in the typical form, being from 

 1 — 1*5 cm. in length and widening steadily to a maximum breadth of 3 mm. The 



Tigs. 215a — e. — ThysanographisHarknessi, var. costatus (Lapw.). tlieCSB alSO are more Closely Set 



■jr, (sixteen to ten in 10 mm.). The 



is 



ventral lacinia occupies a space 

 equal to more than half the 

 width of the central portion of 

 the polypary, and is often pre- 

 served complete. The main ribs 

 of the meshwork originate from 

 the mesial angles of the thecee ; 

 a b c they have at first an ascending 



a. Proximal end, showing well-developed lacinia. Enlarge- direction, but afterwards Curve 



b. Complete specimen^ imii^nff^showing sicula and frag- gleefully Outward and downward, 



mentary lacinia. Dohb's Linn, Hartfell Shales (zone of d finally descend almost Verti- 



Climacog. Wilsoni). Coll. Lapwortli. J 



c. Proximal end with test very attenuated ; clathria and ca ]|y to anas t mOSe with the ex- 



7 I 





lacinia well shown. Dobb's Linn, Hartfell Sliales 

 Lapwortli. 



Coll. 



tremity of the processes immediately 



Figs. 215 d—g. — Thysanograptus Harknessi, var. costatus (Lapworth). 





'■*{-■ 



? 



d e f g 



d. Complete specimen, with lacinia very imperfectly developed. Dobb's Linn, Hartfell Shales (zone 



of Climacog. Wilsoni). Coll. Lapworth. 



e. Scalariform view, showing well-developed lacinia. Hartfell Spa, Hartfell Shales (zone of Climacog. 



Wilsoni). Coll. Lapworth. 

 /. Distal fragment, showing clathriate thickenings. Ibid. 

 g. Broad specimen, doubtfully referable to this form, with paired ventral processes united by flabellate 



membranes (peltas). Dobb's Linn?, Hartfell Shales. Coll. Lapworth. 



