DICRANOGRAPTUS. 



1 65 



Diplograf tidae ; while in the uniserial portion the type of development is thai 

 which obtains throughout the whole of the polypary in Vicellograptus. 



The various species of Dicranograpti can be arranged according to the details of 

 thethecse in groups similar to those of the Vicellograpti. Owing, however, to their 

 frequent imperfect state of preservation, this is often a matter of some difficulty. 



Group I. — Dicranograpti in which 

 the thecse have approximately straight 

 ventral walls and horizontal apertures. 



Group II. — Dicranograpti in which 

 the thecas have gently curved ventral 

 walls and horizontal apertures. 



Group III. — Dicranograpti in which 

 the thecce have gently curved ventral 

 walls, and slightly introverted and 

 introtorted apertures. 



Group IV. — Dicranograpti in which 

 the thecse have strongly curved ventral 

 walls, and markedly introverted and in- 

 trotorted apertures. 



Type Dicranog. Olingani. 

 D. Olingani. 



Type Dicranog. tardiusculus. 



D. tardiusculus. 



D. brevicaulis. 

 Type Dicranog. celticus. 



D. celticus. 



D. rectus. 



Type Dicranog. Nicltolsoni. 

 D. Nicltolsoni. 

 D. cyathiformis. 

 D. ramosus. 



var. spinifer. 

 var. longicaulis. 

 D. zic zac. 

 D. /meatus, var. minim us. 



Group I. — Type Dicranog. Clingani. 



Dicranograpti in which the thecae are of the general Glimacograptus type, having 

 approximately straight ventral walls and horizontal apertures. 



Dicranograptus Clingani, Carruthers. Plate XXIV, figs. 1 a—\ 



1868. Dicranograptus Clingani, Carruthers, G-eol. Mag., vol. v, p. 132, pi. v, figs. 6 a, b, c. 

 1870. Dicranographis Clingani, Hopkinsoii, G-eol. Mag., vol. vii, p. 358, pi. xvi, fig. 4. 

 1876. Dicranograptus Clingani, Lapworth, Cat. West. Scott. Foss., pi. iii, fig. 76. 



Polypary consisting of a very short biserial portion about 2-5— 1 mm. long and 

 two straight uniserial stipes 2 cm. or more in extent, including between them 

 an axillary angle of about 40°. Thecee short, ten in ten mm., of the general 

 Glimacograptus type, with the outer walls straight, and with horizontal 



