DIPLOGRAPTUS. 221 



B. — Diplograpti in which the polypary was almost circular or elliptical in section. 



= Glyptograptus, Lapworth. 



Group I. — Glyptograpti in which Type Glyptog. tamariscus. 

 the axis of the theca was straight, G. tamariscus. 



the thecse semi-circular in section, and var. incertus. 



the apertural margins undulate; excava- G. serratus. 



tions wide and deep. var. barbatus. 



G. t&reiiusculus. 



var. euglyphus. 

 var. sicca t us. 

 G. dentatus. 



var. appendindatus. 

 Group If. — Glyptograpti in which Type Glyptog. siuualus. 

 the axis of the theca was twisted, the G. sinuatus. 



thecee semi-circular in section, and the G. persculphts. 



apertural margins undulate ; excava- 

 tions very distinct. 



0. — Dlplograpti in which the polypary was conspicuously concavo-convex in 

 transverse section. 



= Mesograptus, no v. 



Group I. — Mesograpti in which the Type Mespg.foliaceus. 



thecsB were semi-circular in section and M. foliaceus. 



the apertural margins somewhat mi- M. multidens. 



dulating; excavations deep and con- var. compachis. 



spicuous in proximal region of polypary 71/. modestus. 



only. var. parvulus. 



var. diminutus. 

 M. magnus. 



Group II. — Mesograpti in which the (= Amplexograptus.) 



thecee were semi-circular in section, A. perexcavatus. 



and the apertural margins undulate ; A. confertus. 



excavations deep and conspicuous in A. coelatus. 



the obverse aspect throughout. A. arctus. 



D. — Dlplograpti in which the polypary was tabular in transverse section. 



= Petal ograptus, Suess. 



Group I. — Petalograpti in which the Type Petalog. folium. 

 thecas were typically curved, circular P. folium. 



