186 INFERIOR OOLITE AMMONITES. 



namely, by Gramm. Orhignyi having an umbilicus quite one-fourth larger — whorls 

 narrower and more convex — a more gibbous ventral area — a smaller, and so far as 

 I can find, not hollow, carina — rather coarser ribbing, with the fasciation only 

 very slightly marked — and, lastly, no appearance of inner margin. 



This species has, together with Gramm. fallaciosum and many others, received 

 the name of Am. radians. Now the identification of the species described by 

 Reinecke as Nautilus radians ('Maris Protogsei,' figs. 89,40, 1818) has been an 

 extremely difficult task. It was placed both by Hyatt and by Haug in the genus 

 Grammoceras ; but, when I tried to find anything among my specimens of that 

 genus to agree with Reinecke's figure, 1 was entirely unsuccessful. Several species 

 were something like it, but differed in their quicker coiling — fewer whorls in a 

 smaller umbilicus. Gramm. striatulum was the only species which approached it 

 in the matter of slow coiling, and it seemed probable that " Nautilus radians " 

 was nothing more than a fine-ribbed Gramm. striatulum, in which case the latter 

 name would have been a synonym. 



However, to make sure of the point, I wrote to Dr. Haug, asking him to send 

 me a specimen of what he had identified as Grammoceras radians. With this 

 request he very kindly comphed, and generously presented me with the little 

 specimen shown in the woodcut, fig. 3. I at once saw that I disagreed with my 

 friend concerning the genus of the specimen ; that to my mind it was not a 

 Grammoceras but a Dimiortieria ; that it agreed with many specimens which I had 

 procured from the Jurense-zone of Gloucestershire ; and further, that some of these 

 specimens agreed exactly with Reinecke's figure excepting in the size of the carina 

 (Hang's specimen has a little smaller centre). Reinecke's figure (fig. 2, p. 187) 

 shows the characteristic trait of Dum^ortieria, namely, ribs straight on the lateral 

 area ; but the ribs of Grammioceras are, as the plates show, all slightly bent on this 

 area. We may, therefore, I think, come to the following conclusions :— Either 

 Reinecke delineated the ribs of his specimen incorrectly, and drew the centre too 

 large, and with too many whorls, by which mistakes he made a Grammoceras resemble 

 a Dumortieria ,• or else he drew these points correctly, but made the carina just a 

 trifle too prominent in his fig. 40. Now, to slightly enlarge the carina is a mistake 

 very easily made ; and, considering that it is a case of one slight mistake against 

 three greater errors, I incline to the belief that, in all probability, the specimen 

 Reinecke had before him to draw was a Dumortieria ; and that he was quite 

 correct in drawing the ribs straight across the lateral area. 



In order that my readers may judge of these matters for themselves I have 

 had a woodcut of Reinecke's original figure placed by the side of a woodcut of the 

 specimen Dr. Haug sent me ; and it will be seen that in ribbing the two figures 

 agree exactly ; but that they both differ from Gramm. striatulum (PI. XXVI, figs. 

 7, 9) by wanting the lateral bend of the ribs. 



