DICRANOGRAPTID^E. 



1:;: 



Specific Characters of Farms belonging to the Genus Nemagraptus (Coenograptus). 







Gko 



B I. 





i ..in 



p 11. 



N. graeilii. 



var. remotut 



vnr. lurcularii. 



viir. nitidulus. 



W.explanatui. 





Character of stipes 



Conspicuous 

 sigmoid 



curvature ; 

 numerou 



branches 

 regular 

 intervals 



Irregular 



sigmoid cur- 

 vature ; few- 

 branches, 

 distant from 

 sicula 



Curvature 



upward so 

 that stipes 



cross ; 

 branches as 

 in iV. gracilis 



Irregular 



sigmoid 

 curvature ; 

 one branch 



only, near 

 sicula 



Stipes hori- 

 zontal, 



straight or 

 slightly 



flexed ; one 



or two 



branches 



Stipes 

 straight or 



slightly 



flexed; no 



branches (?). 



Maximum width of stipes . 



■4 — -9 mm. 



•3 mm. 



Y> mm. 



3 mm. 



•6 — - 8 mm. 



"5 — "6 mm. 



Length of sicula .... 



1 mm. 



1 mm. 



1 mm. 



13 mm. 



1 mm. 



12 mm. 



No. of thecse in 10 mm. 



7—9 



10 



7-9 



7 



8 



6—7. 



Inclination 



10°— 15° 



10° 



10° 



10" 



10° 



10°. 



Overlap 



3 <F 



Small frac- 

 tion 



3 



i 



i-k 



*. 



Family DICRANOGRAPTIDjE, Lapworth. 



1873. Dicranograjptidse, Lapworth, Notes on the British Graptolites and their Allies, Geol. Mag., 

 vol. x, table i, p. 555. 



Dicellograptus, sp. 



Uniserial and uni-biserial Graptoloidea with straight or flexed stipes, the 

 angle of divergence always exceeding 180°. 



Thecse tubular, with conspicuous sigmoid ventral curvature, apertural portion 

 more or less isolated; apertures horizontal or in- 

 clined, situated withiu well-defined depressions (exca- 

 vations), and frequently introverted and introtorted. 

 Thecal spines (when present) ventral, mesial. 



The characteristic feature of the Dicrano- 

 graptidee is afforded mainly by the peculiarities of 

 the thecse, as contrasted with those of the families 

 already described. In the Dichograptidse the thecse 

 are simple straight tubes, and their apertures are 

 neither inclined nor introverted, nor are they 

 situated within "excavations." In the Leptograp- 

 tidse the ventral walls of the thecse show slight 

 sigmoid curvature, the apertures are gently inclined 

 and introverted, and open within shallow excavations. In the Dicranograptidae, 

 however, the sigmoid curvature of the ventral wall is typically far more 



18 



Specimen in full relief, showing proximal 

 end (obverse view) and form of 

 thecBe characteristic of the Family 

 Dicranograptidae. Benan Burn, 

 Glenkiln Shales. Coll. Lapworth. 



