258 ANCYLOCERAS, BACULINA. 



ceras. 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 Parkinsonia. 



I place here provisionall}', the small groiip of llacrocephala, 

 the affinities of which await more thorough investigation ; on the 

 one hand their reference to Gosmoceran is indicated by the re- 

 markable resemblance of the last whorls of Cb.sm. 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 Stephanocer-as with nar- 

 row umbilicus. The Macrocep)hala 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 Cosmoceras. 



Forty-two species. 

 CosMOCERAs Calloviense. d'Orb. T. Ill, tigs. BBO, ()(il. Ju- 

 rassic. 



Genus ANCYLOCERAS, d'Orb. 



In the middle Jurassic a number of evolute forms appear, 

 which so fully agree in sculpture and lobular structure with 

 their cotemporary Cosinoceras, that we must, according to the 

 precedent of Quenstedt, regard them as forms of that genus 

 which have become evolute. Strictly considered, one could pro- 

 pose 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 Cosm. ver- 

 rucosum. 



Genus BACULINA, d'Orb. 



In the Sualjiim Qrnata clays, an entirely smooth and straight 

 form of Ammonite appears, which, at the first glance, seems 

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

 smooth initial whoi'ls of the middle Jurassic Ancyloceras are 

 compared with Baculina acuaria, we find that aside from the 



