556 me. l. f. spath on [Dec. 1913, 



change in the course of the radial line at least is prohahly due to 

 incorrect drawings), and another specimen in my collection from 

 Altdorf (Franconia) shows not only a thicker section but also a 

 smaller number of costse, similar to figs. 5 & 6 of Dumortier. 



So far as I am aware, no Mesoliassic forms so thin as this have 

 been described. My specimen has been slightly squashed obliquely, 

 and is worn on one side, but from the inner whorl shown in section 

 I measured the width of the conch to have been at most 7 milli- 

 metres at a whorl-height of 16 mm., precisely the same as in 

 H. bicarinatum (Ziet.). The periphery is tabulate, with a fine 

 median keel, as figured by Keynes on pi. v, fig. 29 (non 27) ; the 

 latter is apparently hollow, and certainly so on the inner whorl, 

 where the section is more rectangular and the keel strong and high. 



' Grammoceras ' celebration Fucini J has evolute whorls and a 

 distant costation. ' GrJ falcicostatum Fuc. 2 is similar, but approxi- 

 mates more closely to the form here described in its thin section. 

 It is possible that the latter may represent an involute development 

 of this falciradiate group. 



In ' Grammoceras ' bassanii Fuc. 3 there is closer and finer 

 costation towards the end, but the curve is only subfalciradiate. 

 Gr. cornacaldense (Tausch) mut. medolense Bettoni, 4 also has sub- 

 anguliradiate costation ; whereas, in the form here described, the 

 radial line is a true Harpocerate sickle with strong forward pro- 

 jection near the periphery. Bettonrs variety, however, somewhat 

 resembles the form here described in its -wide and flat sides and 

 narrow periphery. 



In the absence of suture, or even umbilicus, the identification of 

 this interesting fragment must remain doubtful ; but, as I have 

 stated before, the association with Domerian ammonites makes it 

 probable that it represents a new form, apparently more or less 

 homceomorphons with the typical Toarcian Harpoceras bicarinatum 

 (Ziet.). 



Gen. nov. sp. nov. (?). (PI. LII, fig. 2.) 



1900. Lioceras (?) grecoi Pucini, 'Amm. del Lias Medio dell' Appenn. Centr.' 

 Pal. Ital. vol. vi, p. 65 & pi. xi, fig. 4, 



This interesting fragment was found together with the ammo- 

 nites described in the foregoing pages. Like Fucini's forms it has 

 a much compressed section, but the umbilicus is smaller than that 

 of his fig. 4 a, although not quite so small as that of fig. 5a: 

 this might be explained, according to Fucini, by the intermediate 

 size of my fragment. 



The greatest thickness also occurs at the inner third of the whorl, 



1 'Ammoniti del Lias Medio dell' Appennino Centrale' Pal. Ital. vol. vi 

 (1900) p. 41 & pi. x, figs. 1-2. 



2 ' Cef'alop. Liass. del Monte di Cetona' ibid. vol. x (1904) pi. (xviii) xxxix, 

 fig. 13. 



3 ' Amm. del Lias Medio, &c.' Pal. Ital. vol. vi (1900) p. 46 & pi. x, figs. 6-7. 



4 See p. 554. 



