318 C. Lapioorth — On Scottish Monogr apt idee. 



Normally the hydro thecse are long and slender, widening very 

 slowly in the direction of the aperture, the denticle of which is a 

 little everted ; but examples are sometimes obtained like that given 

 on Plate X. Fig. 9 c, where the exterior margin springs outwards a 

 little below the aperture, and the distal portion of the thecse assumes 

 the form of a minute triangle. When this occurs, the polypary is 

 not unlike Mastrites capillaris, Carr., and, occurring as it does upon 

 the same horizon, is not unfrequently confounded with it. 



Locality. — In the uppe^ portion of the Birkhill Shales, at Mount- 

 benger Burn, Ettrickbridgend, Belcraig, Dobbs Linn, Frenchland, 

 etc. Mr. Hopkinson gives Kirk Gill, Wanlockhead, as a locality 

 for this species. There are no Birkhill Shales in that area, and it is 

 tolerably certain that his specimens are fragments of some forms of 

 Lejptograptidce. 



9. MoNOGRAPTUS Salteri, Gciuitz. Plate X. Figs. 8 a, h. 

 Graptolites tenuis, Salter ; Quart. Journ. Geol. Soc. vol. vii. 



plate X. figs, la, h. 



Polypary slender and slightly curved, one to three inches in 

 length, and with a maximum diameter of one-fiftieth of an inch. 

 Hydrothecse adpressed to the concave margin of the periderm, 30 to 

 the inch, in contact only ; outer margin of each somewhat concave ; 

 denticle inconspicuous, everted. 



This species is characterized chiefly by the gentle curvature and 

 the diminutive size of the polypary. It is remarkable among the 

 Monograjpti in exhibiting a slight crenulation of the dorsal margin, 

 corresponding to the hydrothecse — a peculiarity noticed both by 

 Salter and M'Coy. 



It was described originally by Mr. Salter from specimens 

 furnished by the Girvan beds, but wrongly identified with Mono, 

 tenuis, Portlk. sp. This error was corrected by Professor Geinitz, 

 who proposed its present specific title [Die Graptolitlien, s. 36). 

 It has hitherto remained undescribed. 



Mr. Baily figures some examples of this species with the 

 hydrothecse disposed upon the convex margin of the polj'pary. 

 (Quart. Journ. vol. vii. plate x, fig. la) ; but I have not yet met 

 with forms thus characterized. 



Locality. — M. Salteri is a rare fossil in the Gala Group at Caddon 

 Water Head and Ellwand. It is found in deposits of like age in 

 Piedmont Glen, near Girvan. 



10. MoNOGRAPTus ARGUTUS, sp. nov. Plate X. Figs. 13 a — c. 



Polyparj' five or six inches in length, with a maximum diameter 

 of one-sixteenth of an inch, rigid, arcuate ; proximal extremity 

 strongly incurved. Hydrothecae narrow, adpressed to the concave 

 margin of the periderm, in contact only, 16 to 22 to the inch ; outer 

 margin bent into a double curve ; aperture inclined, and opening 

 partly within the general boundary of the polypary. 



The incurved proximal portion is short, and the normal width of 

 the polypary is attained within the first two inches, and for the re- 

 mainder of its length there is scarcely any further augmentation in 



