150 GENESIS OF THE ARIETULE. 



Caloceras? Deffneri. 



Summ. PI. XI. Pig. 31. 



Amm. Deffneri, Opp., Mittheilungen, II. p. 131, pi. xl. 

 Locality. — Stuttgardt. 



This species has whorls at first sight apparently identical in form with those 

 of the typical Conybeari. 



The young have prominent pilae and geniculas on what seems to be the first 

 quarter of the fourth whorl, and the genicular become tuberculated in the adult, 

 without, however, exhibiting the angular forward bend of Conybeari. 



The abdominal lobe is extremely broad, its lateral branches at first extending 

 over the channel ridges on either side, and then diminishing to two pointed minor 

 lobes. The siphonal saddle is very large. The superior lateral lobes are very 

 narrow, profusely branching, a trifle longer than the abdominal lobe, and very 

 much longer than the inferior laterals. These and the auxiliary lobes are often 

 inclined posteriorly, as in Caloceras. The inferior lateral saddles are about as 

 deep as the superior laterals, and have deeply cut margins, as in that genus. The 

 first auxiliary, however, is often of considerable size, and then the inclined aspect 

 of the inner margin is destroyed. The superior lateral saddles are penetrated by 

 a very peculiar and remarkable marginal lobe, which divides them into two 

 portions, the inner shorter than the outer half. The proportions of the lobes and 

 saddles, and this last peculiarity, show, besides the form, a closer repetition of 

 the characteristics of Conybeari than could have been anticipated from the gen- 

 eral aspect of the shells. 



The channels are shallow, but have lateral ridges, and the keel is well formed 

 and prominent, as in Conybeari. The series of this species in the Museum 

 at Stuttgardt illustrates the different ages at which senile characteristics may 

 begin to appear. The last specimen described above was only 175 mm. in 

 diameter. Another specimen, however, reached the size of 380 mm., and yet 

 only the last volution and a half exhibited senile degradation. The first senile 

 half-volution had obsolescing pilse and tubercles, while the last half-volution was 

 entirely smooth. The channels and keel remained almost unchanged, as in the 

 adidt. Not even a fragment of a living chamber was present. Oppel's original 

 is in the Museum at Stuttgardt. The eighth and ninth whorls of this speci- 

 men are senile, the tubercles have disappeared, the sides are more convergent, 

 and the abdomen more elevated than in the adult; the keel and channels, how- 

 ever, were retained even after the pilae disappeared, though they had become 

 shallower. 



The sutures indicate affinity with the Caloceran series, but our knowledge of 

 the early stages is incomplete, and this opinion is consequently uncertain. 



Neumayr in his " Unterster Lias'' figures a large specimen of Cal. (Arid.) 

 Hqneri, and gives a section. These show that the nealogic stages of this species 

 are first similar to Johnstoni, then as the keel appears resemble Cal. LoJci and the 

 like, and finally take on the narrow channels of the adult. The closely set, bent, 



