CLA.SR V 



CEPHALOPODA G27 



the lobes and saddles, and were as natural and well-founded as the knowledge 



Fio, 1164. 



Vertical sections of ai)tychi belonging to A, CellvXosi {Ammonites zonatus Stopp.) ; B, Imhricati (Ammonite's 

 profundiis Voltz); and C, Punctati {A. imnctatus Voltz). 3/j (after Meneghini and Bornemann). 



of the time permitted. D'Orbigny, Quenstedt, Sandberger and Barrande 

 greatly increased our knowledge of structure and Variation, and defined a 

 number of new genera. 



The next marked epoch dates from the publication of Mojsisovics's great 

 works on the Trias, which made known a fauna as rieh and complex as that 

 of the Jura. Suess, Neumayr, Branco, Waagen, Buckman, Grossouvre, Haug, 

 Diener, Douvillö, Kilian, Zittel, Karpinsky, Hyatt and others made advances 

 of essential importance along difFerent lines. All of these authors attempted 

 to trace phylogenetic histories which of necessity crossed the lines of the 

 older classifications at right angles, and sometimes bridged over the divisions 

 of geologic time. 



Suborder A. INTRASIPHONATA Zittel. 



Family 1. Olymeniidae Gümbel, 



Conchs varying from forms like Anarcestes to those that are more or less compressed in 

 section, and from completely discoidal to compressed and highly involute shells, the surface 

 heing either smooth or ivith large spines. The characteristic ventral saddles are almost 

 imperceptible in some primitive species, and although entire and large as a rule, are 

 in some genera divided by entire ventral lobes. Septa concave along the mesal plane. 

 Siphuncle dorsally situated. Living Chamber occupying about three-fourths of a volution ; 

 aperture with hyponomic sinus. 



The ventral saddles are developed by the obliteration of primitive ventral lobes 

 and fusion of the first pair of saddles (Branco). It is at present questionable whether 

 the ventral lobes of some genera are secondary modifications or retentions of the 

 primitive ventrals, and also whether these can be regarded as divided ventrals even in 

 Gymaclymenia. The antisiphonal lobe is large and long, and often fused with the 

 siphuncular funnels. The dorsal sutures, so far as known, are very peculiar, having 

 only a pair of large saddles confluent with the last pair of external saddles ; or one 

 pair of zygous saddles, and one pair of zygous lobes, the second pair of zygous saddles 

 being confluent with the innermost external pair. 



The Perforation tliroiigh the umbilicus, so constant in Nautiloids, is abeent, and so 

 too are the umbilical depressions on either side of the neck of the protoconch, common 

 in other Ammonoids. The forms are nevertheless ammoniticones, having the proto- 

 conch and other characters of the order. The first septum is described as asellate 

 (Branco), but is tigured as having a broad saddle on the venter. 



Primitive forms similar to Anarcestes, but dift'ering in that tlie sutures have broad 

 entire ventral saddles and broad rounded lobes ; or if the latter are angulated, they 



