504 (7. Lapicorth — On Scottish Monograptidce. 



In the first half of the polypary the thecae are identical in form 

 Tvith those on the fully developed portion of M. Barrandei. Only 

 one-eighth of the length of each is isolated, and that is curved into 

 the ball-like final characteristic of the group. Those on the semi- 

 circular portion of the polypary are isolated for nearly half their 

 length, and the lobe is longer and much more conspicuous. 



locality. — Eare in the Gala Group at Meigle, Buckholm, Gala 

 Hill, Grieston, Cauldshiels, etc. 



Supplementary Species. 



The three following forms are here noticed out of their proper 

 order, owing to the want of sufScient material for complete 

 diagnoses at the time their allies were described. The necessary 

 specimens have since been collected by myself from the South 

 Scottish Silurians. They all belong to the H^alli group, but the 

 third points in the direction of that typified by Monograptus 

 Hishgeri. 



33. MoNOGRAPTTJS Flemingii, Salter, sp. Plate XX. Fig. 8. 

 GraptoUtes Flemingii, Salter ; Quart Journ. Geol. See. vol. viii. 

 pi. vii. figs. 5 a — h. 



Polypary straight and rigid, five or six inches in length, and with 

 an average diameter of one-tenth of an inch. Hydrothecae short 

 and stout, 30 to 36 to the inch, overlapping each other for half 

 their length ; apertural margin convex, everted and produced in 

 a long acuminate and very oblique denticle. 



The sicula in this form is about one-twelfth of an inch in length, 

 and together with the attached portion of the periderm is bent a 

 little backward. There is often a short slender radicular process 

 visible in the line of proximal prolongation of the adherent margin 

 of the sicula. 



The polypary gains its normal width within the first four inches, 

 and for the remainder of its extent it rarely undergoes any further 

 alteration in diameter. 



The hydrothecee, which are far more closely arranged than in any 

 other species of the Halli group, are short tubes slightly contracting 

 distally, and about four times longer than wide. They are in close 

 contact throughout. Near the distal end there is a sudden expan- 

 sion, and the terminal orifice is usually more than twice as broad 

 as the body of the hydrotheca. The edge of the aperture is 

 convex ; the denticle pointed, and a very minute apertural spine is 

 occasionally visible. In the earlier portion of the polypary the 

 denticle is remarkably oblique, frequently making an angle of 150° 

 with the ventral margin. As the polypary increases in length, the 

 obliquity of the denticles gradually diminishes, so that fragments 

 of more than four inches in extent have their final denticles almost 

 horizontal. 



The apparently excessive obliquity of the denticle is due to the 

 peculiar form and great diameter of the thecal aperture. As in 

 M. Halli and If. Biccartonensis, in the earlier thecas the whole 

 extent of the aperture is exposed to view. Its upper and nearest 



