350 C. Laptvorth — On Scottish Monograptidce. 



sea of speculation. From the scantiness and want of detail in their 

 observations, it is useless attempting definitely to correlate them 

 with those conditions observed in the adjoining continent of America, 

 where it has been shown "that the oldest glacial deposits have, 

 yielded evidence of inter-glacial mild conditions " similar to those 

 of the British Isles and Europe (Great Ice-age, Jas. Geikie, p. 428). 

 ( Jb be continued in our next Number.) 



III. — On Scottish MoNOGRAPTiniEj. 



By Charles Lapworth, F. G. S. 



{Continued from page 321.) 



(PLATES XII. AND ZIII.) 



§ IV. 



Group 2. — Type, Monograptus Hisingert, Carr. sp. 



Pohjpary hroad, rigid; bearing overlapping, wn- ornamented, linear or 



cup-like hydrotheccB. 



14. MoNOGRAPTUS HiSTNGERi, Carruthcrs. Plate XII. Figs. la-/. 



Prionotus Sagittarius, Hisinger ; Lethea Suecica, pi. 38, fig. 6. 

 Monograpsus Sagittarius, Geinitz; Die Graptolithen, Taf. ii. figs. 



2, 3, 4, 6, 21. Kichter, Zeitschrift d. Deutsch. Gesellsch. 



1853, Taf. xii. fig. 19. 

 Graptolites Griestonensis, Nicol ; Quart. Journ. Geol. Soc. vol. 



vi. p. 64. 



Polypary four or five inches in length, straight or very slightly 

 curved, attaining a maximum diameter of one-twelfth of an inch. 

 Hydrothecse short and broad cups, with subquadrangular section, 

 20 to 24 to the iuch, without overlap, inclined at an angle of about 

 45° ; outer edge convex distally, proximally impressed ; apertural 

 margin deep, concave, at right angles to the general direction of the 

 theca ; denticle triangular and inornate. 



The sicula in this species is short and broad, and the proximal 

 portion of polypary is consequently very abrupt. The polypary 

 itself is usually quite straight throughout the whole of its extent, but 

 sometimes there is a decided ventral curvature. The hydrothecte 

 afford the best characteristic of the species ; they are short and broad 

 cups, sacculate distally and proximally compressed, with a broad 

 concave or straight apertural margin, which as a rule is placed per- 

 pendicular to the general direction of the theca. The sharply im- 

 pressed proximal moiety of the outer edge forms a broad excavation, 

 the deep apertural margin occupying nearly half the transverse* 

 diameter of the polypary. This hollow is so strongly marked, that 

 in some views the ventral margin appears as if it were cut into a 

 series of deep notches. An example of this nature seems to have 

 been the original foundation for Nicol's description and figure of his 

 Graptolites Griestonensis {Joe. cit. supra). The denticle is sometimes 

 ornamented with a very minute spine, which is slightly inclined. 



