MONOGRAPTUS. 



495 



Figs. 350a — c. — Monograptus {Rastrites) 

 maximus (Carruthers). 



Poljpary slightly arcuate, with thecae on the convex margin ; " common body " 

 reduced to a mere thread throughout. Thecse three to two in 10 mm., very 



long, commonly two to two and a half times 



as long as the interspace between them, 



steadily increasing until a length of 1*8 cm. 



is attained ; slightly declined, with triangular 



base and distinctly retroflexed apertural 



region. 



Description. — The polypary is only known in 



fragments ; it must, however, be by far the largest 



contained within the group, the great length of the 



thecae and their relative robustness as compared 



with the common body being unique. 



The proximal end is characteristic ; the sicula is 

 small and inconspicuous ; tli. 1 measures only 1'5 

 mm., but the increase in length of each succeeding 

 theca is most marked, th. 2 measuring 3"5 mm, th. 

 3, 5 mm. 



While the interspaces between the first three 

 thecse measure 1'5 mm. and 3 mm. respectively, a 

 later stage shows the thecse increasing to a length 

 of 1"3-1"4 cm. with interspaces of about 6 mm. and 

 it would seem as if the thecse continued to increase 

 still further, for fragments are known in which 

 the thecse measure 1"8 cm. in length with inter- 

 spaces of 10 mm. The aperture is situated close 

 to the extremity of the theca, which shows distinct 

 retroflexion (figs. 350 a and h). 



Affinities. — Monog. {Rastrites) maximus is un- 

 doubtedly closely allied to M. (B.) Linvsei, and 

 certain fragments of it would probably be hard 

 to distinguish from fragments of that species. It 

 is clear, however, that in M. (B.) maximus (unlike 

 M. [Z?.] Linngei) the increase in length of the thecae 

 is persistent, and the thec^ attain an extent never 

 reached by those of M. (B.) Linnsei. The proximal 

 end of M. (B.) maximus also is different, the thec^ 

 lengthening far more rapidly than is the case with those of M. (B.) Linnsei. 



Horizon and Localities. — Gala-Tarannon M. (B.) via.rimus band in zone of M. 

 turriculatus) . 



8. Scotland : Berrybush Burn ; Belcraig Burn ; Dobb's Linn ; Thirlstane 



65 



a and h. Proximal thecae (referable pro- 

 bably to this species), showing the 

 marked retroflexion of the apertural 

 region. Belcraig Burn, S. Scotland ; 

 Upper Birkhill Shales. Coll. Wood. 



c. Two distal thecae. Enlargement of 

 part of PI. L, fig. 6 6. 



