THE GRAPTOLITES AND CORALS 293 



higher diplograptid stage and may be compared with 

 those early nautiloids (Lituites, etc.), which show uncoil- 

 ing before coiled forms had become well established ; 

 while Di, sllograptus shows only an intermediate stage 

 without any anagenesis. The latter has the range of the 

 family, while the former is Llandeilian and Caradocian 

 only. 



Family DIPLOGRAPTID/E. Biserial, with straight un- 

 branched stipes. Thecae tubular, usually in contact for 

 a large part of their length. Range: Middle Skiddavian 

 to Upper VaLentian, with acme from Caradocian to 

 Middle Valentian. 



Two genera are usually recognized. CUmacogvaptiis 

 (Fig. 86) is characterized by the sigmoid curvature of the 

 thecae, and its ' excavations "; Diplogvaptus (Fig. 88, /, g) 

 has straight or nearly straight thecae, overlapping and with 

 aperture everted (turned outwards). The latter has been 

 subdivided into several sub-genera. Dr. Ruedemann of the 

 New York Geological Survey has discovered specimens 

 showing that Diplogvaptus lived in clusters hanging from 



FIG. 88. VARIOUS GRAPTOLITES. 



a, Dictyonema flabelliforme (Eichwald), Tremadocian. Part of polypary, 

 with sicula and nema. (Natural size.) (Full length over 80 mm., 

 maximam width 75 mm.) b, Leptograptus Jlaccidus (Hall), Carado- 

 cian. (XT-)- S, Sicula. c, Nemagraptus gracilis (Hall), Llandeilian. 

 (Xj.) d t Dicellograptus gurleyi Lapworth, Llandeilian, New York. 

 (Xf.) e, Dicranograttus nicholsoni Hopkinson, Llandeiliaa-Carado- 

 cian. (f.) /, Diplograptus (Petalograptus) palmeus van tenuis 

 (Barrande), Valentian. S, Sicula ; V, virgula. g, Diplograptus 

 foliaceus M'Coy, Llandeilian, New York. Floating colony. (Natural 

 size.) (After Ruedemann. ) Pn, Pneumatophore (float) ; G, gonangia 

 (reproductive vesicles) ; P\, first generation of polyparies ; /*$ second 

 generation ; V, virgula. h, Monograptiu cyphus Lapworth, Lower 

 Valentian. Thecse near proximal end. i, M. sandersnni Lapworth, 

 Valentian. Distal thecae. j, M. vomerinus (Nicholson), Salopian. 

 Thecae near proximal end ; in full relief, showing torsion of thecal axis. 

 k, M. lobiferus (M'Coy), Valentian. Distal thecae. /, M. convolutus 

 (Hisinger), Valentian. m, M, (Rastrites) longispinus Perner, Valen- 

 tian. (Allxf. unless otherwise stated.) a, e, g, After Ruedemann; 

 b, d, from Ruedemann, after Lapworth; c, from Ruedemann, after 

 Hall ; remainder after Elles and Wood. 



