82 DK. L. F. SPATH ON THE AMMONITES [vol. lxxix, 



have not been found by Dr. Lang. It is interesting to note that 

 many of the examples of Microderoceras birchi are malformed. 



In the ' birch i-t&bul&Y ' bed, immediately above the birchi- 

 nodular, the number of individuals of M. birchi is very great; but 

 they are generally of small dimensions, and associated with 

 Arietites turneri and Xipheroceras. 



(I) Genus Xipheroceras S. S. Buckman. 



This genus is abundantly represented in the ' bircTii-tsibulax ' at 

 the upper limit of the section here described. The commonest 

 form has an oval compressed section, and may be identical with 

 the crushed Ammonites capricomoid.es of Quenstedt, 1 for this also 

 seems to have the ventral differentiation of the costse far less 

 pronounced than the later Xipheroceras planicosta (Sowerby) : 

 that is to say, there is neither a distinct latero-peripheral angle, nor 

 appreciable flattening of the costae on the venter. The inner 

 whorls may remain smooth or slightly striate to a comparatively 

 large diameter, and consequently distinction of very young- 

 examples from the equally smooth Microderoceras birchi, with 

 which they are associated (but which has a much more complex 

 suture-line), is not always easy. The inner whorls, however, are 

 rather variable, as they are in the later X. planicosta, and some 

 examples, transitional to the true X. planicosta, occur alreacty in 

 the ' &£>c/u -tabular.' 



Both the genus Xipheroceras and the less simplified Micro- 

 deroceras, dealt with above, are included in the family Deroceraticke. 

 It is probable, as Prof. Haug thinks, 2 that this family is derived 

 from Lytoceratida?, and has no connexion with, for example, Para- 

 caloceras centaitroides (Savi & Meneghini), remarkable for its 

 ' retarded ' inner whorls, with which, after Canavari, 3 I was at one 

 time inclined to connect Microderoceras. 4 ' 



The suture-line development of both Xipheroceras and Micro- 

 deroceras was worked out, and the suture-line of M. birchi, at 

 25 mm. diameter, shows great resemblance to that of. for instance, 

 Ectocentrites herbichi (Bonarelli) as figured by Vadasz, 5 whereas 

 in, for example, Deroceras \_Derolytoceras'.^pecchiolii (Meneghini) 

 Fucini 6 the oblique second lateral saddle is indicated, although 

 the high siphonal lobe still retains its Lytoceratid character. At a 

 diameter of 10 mm., the suture-line of M. birchi is close to that 



1 ' Ammoniten des Schwabischen Jura ' 1883, pi. xvii, fig. 11. 



2 ' Traite de Geologie ' vol. ii, fasc. 2 (1910) p. 950. 



3 Op. cit. 1882, p. 190 (68). 



4 'Notes on Ammonites' Geol. Mag. 1919, p. 175. 



5 ' Unterliasische Fauna von Alsorakos. &c.' Mitt. Jahrb. K. Ung. Geol. 

 E eichsanst. vol. xvi (1908) pi. ix, fig. 4a: 'JEgoceras adnethicum (Hauer) 

 var. involuta, nov.' 



G ' Cefalopodi Liassici del Monte di Cetona ' pt. iii (1903) p. 179, pi. xxiv 

 (xxxv), fig. 12 & pi. xxvii (xxxviii), figs. 3-7, p. 181, text-fig. 102. (The genus 

 Derolytoceras Ecsenberg ought really to include only the Uomerian forms.) 



