34 



ventral lobe. The saddle occupying the center of the short, 

 ventro-lateral curve is acute at the summit, having a height one- 

 fourth greater than the width at the base, and curving a little 

 more abruptly on the ventral side. The ventral lobe extends 

 about half the depth of the adjacent air-chamber, and is abruptly 

 narrowed below, the walls being essentially parallel and coincident 

 with those of the siphuncle. The septa are thin in the center, 

 thickened and imbricating at the margins, leaving a deeply marked 

 suture line." 



The definition is from Hall's Palaeontology of New York, vol. 

 5, pt. 2, p. 433, and it will be observed, that it includes all the 

 characters ascribed to the genus. If the large size, involute 

 whorls and complicated chambers do not indicate a fully developed 

 Goniatite, we would like to know what later species took on 

 characters belonging to a higher stage of animal development. 

 We know there are some more recent species having more angles 

 in the septa, and others with fewer angles, but the increase or 

 decrease, in the number of these, will hardly be held to indicate 

 a higher or lower stage of the development of the animal; for, if 

 so, we need only to turn our attention to angles in the septa, to 

 rate the species in the grade of its animal existence. If the stage 

 of the involution is the measure of the perfection of the animal, 

 then this species reached the highest grade, for the outer volution 

 embraces all the inner ones, and, we cannot assume the contrary, 

 because no older cephalopod ever embraced the inner whorls, in 

 the outer volution, and closed the umbilicus. 



What these facts tend to prove is that, so far as we know, the 

 most ancient specimen belonging to the family Goniatitidce that 

 has ever been found in America was as highly developed as an 

 animal and in the structure of its shell, as any more recent 

 specimen. Prof. Hyatt raises the Tetrabranchiata to the grade of 

 a subclass and divides it into the orders, Nautiloidea and Am- 

 monoidea and refers the family Goniatitidce to the Order Am- 

 monoidea. This is probably a good classification, but it does not 

 alter the conclusions to be drawn from the facts we are presenting. 

 His idea, however, that "The efforts of the Orthoceratite to adapt 

 itself fully to the requirements of a mixed habitat of swimming 

 and crawling gave rise to the Nautiloidea, and the efforts of the 

 same type to become completely a littoral crawler evolved the 

 Ammonoidea" does not meet with any support from the shells 

 that have been discovered belonging to the Goniatitidce. One can 

 imagine that from Orthoceras through Cyrtoceras, Gyroceras and 

 other genera arose the Nautilidce y but there is absolutely no con- 



