THE FAUNA OF THE ST. JOHN GEOUP. 139 



of the species is the one which is most common, and appears to represent most completely 

 the characters of the species as seen in the examples studied by Prof. Hartt. The ante- 

 rior marginal fold is more distinct than would be supposed from Hartt's description, but 

 in other respects his description agrees. 



The following characters may be given in addition to the original description by the 

 author of the species in " Acadian Geology " : — 



Movable Cheeks. — These are similar to those of L. tener, but the intramarginal ridge is 

 less marked. The width is about one-third of the length, including the attached exten- 

 sion of the anterior marginal fold ; the inner area of the cheek is about three times the 

 width of the marginal fold, and is fully twice as long as wide ; the outer part of its 

 slope forms a hollow or furrow behind the marginal fold. The folded margin of the 

 cheek ends backward in a triangular lappet similar to that of i. tener, but smaller in propor- 

 tion. The thorax of this species has not been recovered, nor is the pygidium known. 



Sculpture. — This is very fine, and consists of a minute pitting of the surface of the test, 

 the markings being so fine that the test has a smoother and more shining surface than 

 other species associated with it. The anterior marginal fold of the movable cheeks, outside 

 of the sharp ridge along its inner side, is marked by from four to live parallel raised lines, 

 similar to those of the preceding species, but finer. 



Length of head-shield, 2 mm. ; width of middle piece, Vl mm. Length of movable 

 cheek, 11 mm., width, 4 mm. 



Horizon and Locality. — In the grey shales of Div. 1 (r at Portland ; also in same beds 

 at St. Martin's. 



The following varieties have been observed. 



Var. IMMAEGINATA (PI. I, figs. 4 ft to d.) 



This has a broad channel in front of the glabella and cheeks, and a sharply upturned 

 anterior edge, not impressed by the marginal fold. The ocular fillet and glabellar furrows 

 are distinctly visible on the mould of the inner surface, and the glabella is conical. 



Horizon and Locality. — In the grey shales of 1 c -, at Portland and St. Martin's. 



In the absence of the anterior marginal fold, the prominence of the ocular fillet, the 

 ridging of the surface of the fixed cheeks, the conical glabella, and the position of the 

 glabellar furrows, this form approaches L. tener. 



Var. Aurora (PI. II, figs. T a to /.) 



Conocephalites Aurora, Hartt. 



This variety has a less conical glabella than the type, is much depressed in front of 

 the glabella and cheeks, and possesses a narrow anterior marginal fold ; the channel 

 behind the fold is narrower than in the preceding variety, or in the type ; the glabella is 

 prominent and the ocular fillet distinct on the mould of the head ; the two central furrows 

 of the glabella are transverse and not turned backward, as in the two preceding forms. 



Horizon and Locality. — Same as preceding. 



In the short space in front of the glabella, the upturned anterior margin and the oval 



