12 



TYPE AMMONITES— VI Feb. 



This theory of substitution, with consequent confusion, is not in 

 the least unreasonable, for it is fully borne out by what Bird did in 

 regard to A . clevelandicus and A . elegans, as already noticed in this work, 

 Vol. II, No. 109. 



The figure in the first edition is, therefore, a synthetograph — the 

 specimens which have been used in the drawing of it become 

 syntypes of the species : they are presumed to be the ventrally sulcate, 

 a Schlotheimian and the carinate-bisulcate, an Asterocerate — which 

 should be chosen as lectotype ? The evidence of subsequent authors 

 who have had opportunity to study Young & Bird's material may be 

 given. 



Simpson, M., 1843, A Monograph of the Ammonites of the York- 

 shire Lias. 



" [P- 55] IV. With a dorsal furrow only. 



" 107. A. Redcarensis, Y. & B. 



" Depressed ; volutions 5 or 6, inner ones J concealed, outer whorl 

 rather more than | the diameter ; radii prominent, diverging, straight 

 along the sides of the whorl, then suddenly bend towards the aperture 

 near the back, where they are terminated by a narrow, smooth space 

 or furrow ; aperture triangular, or sub-quadrate ; diameter 3 inches. 



" The radii proceed from the inner margin of the whorls, and have 

 the appearance of coarse plaits ; the prominent angles on the back, 

 and the absence of a keel, render this a highly characteristic species ; 

 the sides of the whorls are slightly convex, and the inner edge quickly 

 rounded. From the appearance of the matrix I judge it to be from 

 the ironstone series ; I have a fragment of this species from the oolite 

 of Filey : the flat space on the back is very narrow, and the radii are 

 much more numerous and slender than in the lias specimens." 



Simpson, M. The Fossils of the Yorkshire Lias, 1855, pp. 100, loi. 



" [P. 100] IV. With a dorsal furrow only. 



" 187. A. REDCARENSIS, Y. & B — Volutions 5 or 6, [p. loi] inner 

 ones ^ concealed, outer whorl rather more than J the diameter ; radii 

 prominent, diverging, straight along the sides of the whorl, then suddenly 

 bend towards the aperture near the back, where they are terminated 

 by a narrow smooth space or furrow ; aperture triangular, or sub- 

 quadrate ; diameter 3 inches." 



" The radii proceed from the inner margin of the whorls, and have 

 the appearance of coarse plaits ; the prominent angles on the back, 

 and the absence of a keel, render this a highly characteristic species ; 

 the sides of the whorls are slightly convex, and the inner edge quickly 

 rounded." 



" I have now got Young's original Redcar specimen, and I see no 

 difference between it and A. anguliferus. Ph. It is a very variable 

 species. In some the outer whorl is narrower, and the ribs on the back 

 are so depressed as to shew the flat space as a keel ; in others they are 

 so prominent as to form a narrow channel. Some specimens are much 

 inflated, whilst others are much depressed. Mr. Bird's figure is entirely 

 erroneous, and must be intended to represent A. obtusus. Sow. 



" I have a fragment of a specimen, twice as thick as some, and 

 with coarse and irregular radii. I leave it at present as a variety. — 

 L.L." 



