496 



BRITISH GRAPTOLITES. 



Specific Characters of Forms belong- 











GROUP I.-A. 



(UNIFORM 



. 









21. cyphui. 



3f. acinacei. 



M. gre- 

 garius. 



3f. bokemicug. 



31, con- 

 cinnus. 



3f. Niliioni, 



M. leptotheca. 



3£. regularis. 





Character of polypary 



Arcuate, 

 with 



involute 

 proximal 



portion 



Straight, 



with arciiate 



proximal 



portion 



Short, 

 arcuate 



Straight, 



broadly 



rounded 



proximally 



Ventral 

 curvature 



Straight, 



with 

 double cur- 

 vature of 

 proximal 

 portion 



Straight 



Straight and 

 rigid 





Maximum width 



15 mm. 



2 mm. 



•75 mm. 



2 mm. 



1 mm. 



1 mm. 



3 mm. 



I'o mm. 





Length of sicula 



4 mm. 



5 mm. 



5 mm. 



1 mm. 



— 



15 mm. 



— 



■7 mm. 





Characters of thecee : 

 1. No. in 10 mm. 



10—9 



6-11 



10 



11-9 



12—10 



8—9 



8—10 



12—8 





2. Overlap .... 



i-f 



h-i 



0-4 



l-i 



4-i 



i 



3 



4 



Slight— 1 





3. Apertural margin . 



Even, 

 normal 



Even, 

 everted 



Even, 

 normal 



Wide, 

 normal 



Wide, 



even, 



everted 



Even, 

 horizontal 



Even, hori- 

 zontal 



Wide, even, 

 slightly 

 everted 





4. Proportion length to 

 width (mature) 



6 : 1 



10 : 1 



5 : 1 



2—3 : 1 



3 : 1 



4—5 : 1 



25 : 1 



9 : 1 



1 



Character of polypary 



Maximum width 

 Length of sicula 



Characters of thecse : 



1. No. in 10 mm. 



2. Overlap (a) 



„ (B) . . 



3. Apertural margin (a) 



. (B) 



4. Proportion length to 

 width (mature) 



GROUP I.— B. (BIFORM). 



Jjf. revo- 

 lufug. 



Arcuate, 

 with 



broadly 

 recurved 

 proximal 



portion 



1 mm. 



8—10 

 Slight 



Eetro- 

 verted 



Even 



7 : 1 



var. aus 

 terns. 



Arcuate 

 through- 

 out 



var. prs- 

 cursor. 



II. difformis. 



Tendency 

 to isolation 



Arcuate, 



with 



involute 



proximal 



portion 



1 mm. 

 1 mm. 



12—10 

 Slight 



Eetroverted, 



isolated 



Even and 

 slightly 

 everted 



3i". argejiteiis. 



var. cygneus. 



Straight, 



with abrupt 



proximal 



curvature 



2-5 mm. 

 1 mm. 



15—11 

 Contact 



Eetroverted 

 and isolated 



Even 



Narrower 



than 



typical 



species 



1'5 mm. 



M, limatiilus. 



Arcuate or 

 straight, 



with stiffly 



recurved 



proximal 



portion 



1 mm. 



With very 

 long virgella 



12 



Contact 



Slightly 

 retroverted 



Even, 

 everted 



M. colojius. 



4 : 1 



Straight, 



with ventral 



proximal 



curvature 



2-3 mm. 



1-6 mm. 



12—10 



Ogee curva- 

 ture and 

 retroverted 



Even, 

 normal 



4: 1 



A. Eefers to proximal type. b. Kefers to distal type. 



