124 TF. H. Hudleston—Tlie Yorkshire Oolite. 



"VVydale species. The specimen towards tlie last wliorl is in- 

 differently preserved. 



Relations and Distrihdion. — The differences between this form 

 and the more typical PL Miinsteri are, that this one has a narrower 

 spiral angle, and has the whorl distinctly bicarinated, and each 

 whorl is less completely overlapped by the succeeding one, so that 

 the sutural excavation is more marked. On the other hand, it 

 resembles the types of that species in having the ornamentation 

 reticulated rather than granulated, that is to say, the transverse ribbing 

 is not cut through sufficiently deeply to produce a very distinct 

 granulation, though there is an approach to it in some places. 



With respect to distribution this must be viewed as representing 

 PI. Miinsteri in the higher beds. It is clearly a Kimmeridge form, 

 though I cannot find it noticed on the Continent from beds of that 

 age. Eare in the Coral Eag of the Howardian Hills. 



53. — Pleurotomakia Agassizii, Mtinster, ISM. Plate IV. 

 Figs. 4a, b. 



Pleurotomaria Agassizii, Miinster, Goldfuss, 1844, pt. 3, p. 71, pi. 186, fig. 9. 



Idem Idem, B'Orbigny, 1852, Terr. Jurass. vol. ii. p. 572, 



pi. 426, figs. 1-5. 



Bihliograplmj, etc. — Miinster's species was from the Corallenkalke 

 of Nattheim. His description is not very close, but the figure 

 (enlarged) is fairly like the specimen now under consideration. 

 That this is the species intended by D'Orbigny there is every 

 reason to believe, as his description in most respects tallies with the 

 North Grimston specimen, though his figure, which is almost too 

 good for a fossil, is somewhat different. 



Description. — Specimen from the Coral Eag of North Grimston 

 (Strickland Collection). 



Length 72 millimetres. 



Width 60 ,, 



Spiral angle 60". 



Shell conical, trochiform, umbilicated. Spire composed of about 

 nine whorls (seven now remain without the apex). These, with the 

 exception of the last whorl, increase under a regular angle, and are 

 so close, towards the apex, that the suture can with difficulty be 

 made out. They are nearly flat, and down to the margin of the 

 penultimate form an almost unbroken cone. The penultimate is 

 rather swollen, and the last whorl is obtusely angular. The 

 ornaments vary in different parts of the shell. In the posterior 

 whorls the closely -set transverse ribbing is fine and rather granular. 

 Anteriorly the system of transverse costas is wider apart, sometimes 

 granulated, sometimes almost continuous, but on the whole irregular 

 .and coarsish over the entire surface of the two last whorls. A 

 characteristic feature is a double row of thick rough tuberculations, 

 which become very prominent in the anterior whorls. Between these 

 the imbricated band of the sinus is conspicuous, occupying a 

 postion a little above the middle of each whorl. The base is nearly 

 flat, and has the irregular ornamentation of the rest of the body- 

 whorl without the tuberculations. The sides of the umbilicus are 

 steep, and the columella but slightly inclined outwards. 



