258 ANCYLOCERAS, BAd UNA. 



cerax. which seems to be completed in the Parkinsonia. In 

 respect to the genetic relationship with the Parkinsonia, the 

 inner whorls of the Runcinata are above all decisive, which, as 

 is well known, possess the characters of the Purl.-infunria. 



I place here provisionally, the small group of Macrocephala, 

 the affinities of which await more thorough investigation ; on the 

 one hand their reference to Cosmocera* is indicated by the re- 

 markable resemblance of the last whorls of Coxm. Gallilaeii, 

 while on the other the inner whorls of the Macrocephala present 

 no trace of the siphonal furrow, and also in form and ribbing much 

 analogy exists with inflated species of Stephanoceras with nar- 

 row umbilicus. The Macrocephala are strangers in the European 

 Jurassic fauna, which, in our part of the world appears only for 

 a short time ; when we have learned to know more accurately 

 their ancestral limits, only then will a distinction be possible. 

 and probably it will be necessary to establish a distinct genus for 

 their reception. Preliminarily I will regard them as Cotsmoceras. 



Forty-two species. 



COSMOCERAS CALLOVIENSE, d'Orb. T. 111. tigs. r>(H). (id. Ju- 

 rassic. 



Genus ANCYLOCEEAS, d'Orb. 



In the middle Jurassic a number of evolnte forms .-ippear. 

 which so fully agree in sculpture and lolmlar struct nre with 

 their cotemporary Cosmoceras, that we must, according to the 

 precedent of Queiistedt. regard them as forms of that genus 

 which have become e volute. Strictly considered, one could pro- 

 pose 1 a new name for them, but to avoid this, it appears to the 

 purpose to adopt the name Ancyloceras. which has become 

 vacant amongst the cretaceous Ammonites since they have been 

 hitherto placed in this genus. The quite smooth initial whorls 

 are very striking, a character which also appears in O >*///. n-r- 

 rucosum. 



BACULINA, d'Orb. 



In the Suabian Ornata clays, an entirely smooth and straight 

 form of Ammonite appears, which, at the lirst glance. seems 

 quite enigmatical and of uncertain reference. If, however, the 

 smooth initial whorls of the middle Jurassic, Ancyloceras are 

 compared with lltn-nliim acuaria, we find that aside from the 



