296 BRITISH GRAPTOLITES. 



The mode of development of the earlier thecre is in all essentials similar to that 

 in the Diplograptidae ; but th. I 1 , and occasionally th. I 2 , grow almost vertically 

 downward for the greater part of their length and only bend upward in the 

 immediate region of the aperture. In this respect the Gryptograpti show an 

 approach to the mode of development of some of the Dichograptidse (Phyllogra/ptus). 



The test is remarkably attenuated, and in this respect seems to indicate an 

 approach to that of the GrlossograptidsG. In some examples it has the appearance 

 of being punctate. 



The type species of Gryptograptus is G. trienrnis, and there can be little doubt 

 that Nicholson's Diplograptus Hophinsoni really belongs to the same genus; it is 

 probable also that the forms from the Skiddaw Slates referred to Climacog. anten- 

 narius by many authors should also be included, though they are so indifferently 

 preserved that it is not possible to be certain of this. The known British forms of 

 G ' ryptograptus are : 



Gryptog. tricornis, G. Hophinsoni. 



var. SrJiaferi. G. (?) antennarius. 



Cryptograptus tricornis (Carruthers). Plate XXXII, figs. 12*7 — d. 



1859. Diplograpsus tricornis, Carruthers, Ann. Mag. Nat. Hist. [3], vol. iii, p. 25. 



1859. Oraptolitkus marcidus, Hall, Pal. New York, p. 514, figs. 1, 2, 3. 



1867. Diplograpsus tricornis, Carruthers, Intell. Observer, p. 290, pi. i, figs. 7, 8, 10. 



1872. Diplograptus Etheridgii, Hopkinson ?, Geol. Mag., vol. ix, p. 504, pi. xii, figs. 5 a — e. 



1875. Diplograptus tricornis, Lapworth, Quart. Journ. Geol. Soc., vol. xxxi, p. 658, pi. xxxv, 

 figs. 6 a and b. 



1876. Diplograptus tricornis, Lapworth, Cat. West. Scott. Foss., pi. ii, fig. 39. 



1877. Diplograptus tricornis, Lapworth, Proc. Belfast Nat. Field Club, p. 132, pi. vi, fig. 10. 

 1880. Cryptograptus tricornis, Lapworth, Ann. Mag. Nat. Hist. [5], vol. v, p. 171, pi. v, fig. 27 a— e. 

 1908. Cryptograptus tricornis, Ruedemann, Grapt. of New York, pt. 2, p. 443, pi. xxviii, figs. 1 — 4, 



and text-figs. 410—422. 



Polypary, with very attenuate test, 2 — 4 cm. in length, widest at base, having 



a maximum width of 1'5 mm., but typically narrower. Sicula very long, 



3 mm. in length. Virgella and straight lateral spines conspicuous. Thecas 



eleven in 10 mm., about 1 mm. in length, overlapping one half their extent, 



with very short free edge, occasionally rounded off; apertural edges 



everted, giving an appearance of crenulation to ventral margin of polypary. 



Description. — The dimensions and general appearance of the polypary vary 



considerably according to the direction of compression. In the obverse aspect the 



polypary rarely exceeds 1 mm. in width, and the thecal apertures can, as a rule, 



be clearly seen, but the spines at the base are not conspicuous. In the reverse 



aspect the polypary is frequently 1*5 mm. in breadth, no thecal apertures can be 



