SPECIES OF CAEB0NIFEK0X7S MTJECHISONIA. 571 



Mtjechisonia (Hypeegonia) plana, sp. nov. (PI. XVI. figs. 14, 15.) 



Shell elongated, turreted, composed of about thirteen very angular 

 whorls. Angle considerably below the middle of the whorl, bearing 

 a strong keel. Upper part of the whorl very flat, ornamented with 

 two much finer keels, between which there is a wide space, as one 

 keel is immediately below the suture and the other at a slight dis- 

 tance above the angle. Below the angle is another keel, not so 

 strong as that on the angle, but stronger than those above it ; this 

 keel is visible just above the suture on the upper whorls. Sinus 

 most probably situated between the strongest keel and that next 

 above. Lines of growth not discernible. Base flattened. Colu- 

 mella simple. 



The only shell to which this bears any resemblance is M. amcena, 

 De Kon.,^ from which it may be easily distinguished by its more 

 elongated form and more angular whorls. The keels are also some- 

 what diflerent, both in their form and their disposition. On this 

 species the keels stand out clear and sharp, whilst on M. amcena 

 they are so strong and rounded as to make the spaces between 

 appear like grooves. On the base of M. amcena there is also an addi- 

 tional keel, and the uppermost one is absent. 



Length of specimen figured 9 millim. ; height of two lower whorls 

 3 millim. ; width of penultimate whorl 2J miUim. 



Another shell, which is imperfectly preserved, and of which the 

 apex is broken so that only eight whorls remain, measures 10 millim. 

 in' length. 



Locality. Law Quarry, Dairy ; Craigenglen, Campsie. 



Formation. Shales in the Lower Limestone Series. 



Mtjechisonia (Hypeegonia) elongata, Portl. (PI. XYII. figs. 2, 3.) 

 Murchisonia elongata, J. E. Portlock, 1843, 'Geol. Rep. on London- 

 derry,' p. 569, pi. xxxviii. fig. 10 a, h; F. M'Coy, 1844, ' Syn. Garb. 

 Foss. Ireland,' p. 42; H. G. Bronn, 1848, ^ndex Pal.' p. 747; J. 

 Morris, 1854, ' Cat. Brit. Poss.' p. 259 ; H. Griffith, 1860, Journ. 

 Geol. Soc. Dublin, vol. ix. p. 90 ; J. J. Bigsby, 1878, ' Thes. Dev.- 

 Carb.' p. 325 ; R. Etheridge, 1888, ' Foss. of Brit. Islands,' vol. i. 

 Pal. p. 301. 



Shell elongated, turreted, composed of from ten to twelve whorls. 

 Whorls angular; surface nearly flat, both above and below the angle. 

 Sinual band situated about the middle of the body- whorl and a little 

 below the middle of the upper whorls ; it is narrow and bounded by 

 two keels, generally about equal in strength, but sometimes the 

 lower keel is more strongly developed on the anterior whorls. Orna- 

 mentation consisting of two fine keels above the band and two 

 stronger ones below, with one or two finer additional keels on the 

 body -whorl and occasionally a fine thread in the middle of the 

 band. Sutures deep. Lines of growth fine, distinct, and slightly 

 irregular, strongly arched on the band. Base convex. Mouth 

 unseen. 



^ * Faune du Oalc. Carb. de la Belgique,' vol. viii. pt. 4, p. 22, pi. xxxiy. 

 figs. 32-34. 



Q. J. G. S. No. 192. 2 b 



