430 



CEPHALOPODA. 



[XKN. — ZON. 



schohariensis, Castelnau, 1843, Syst. Sil., p. 

 35. Not recognized, 

 stevensana, Meek & 

 Worthen, 1866, Geo. 

 Sur. 111., vol. 2. 

 p. 382, Up. Coal 

 Meas. 



Xenophora, Fischer, 1806, 

 Museum Demidovia- 

 num, p. 213. Not an 

 American Palaeozoic 

 genus. 

 antiqua, see Pseudo- 

 pliorus antiquus. 



Zaftyghtos, Walcott, 

 1884, Monogr. U. S. 

 Geo. Sur., vol. 8, p. 

 263. Shell minute, 

 elongate ; aperture 

 large, oblong, nearly 

 vertical ; outer lip 

 thin ; collumellar lip 

 reflected, plicated ; 

 surface marked by 

 slightly oblique 

 vertical striae. 

 Type Z. carbonariu8. 



Fig. 723.— Zaptychius 

 carbonari us. 



carbonarius, Walcott, 1884, Monogr. U. S. 

 Geo. Sur., vol. 8, p. 263, Subcarbonif- 

 erous. 



Fio. T24.— ZonitespriM-u- 



Zonitks, Montfort, 1810, Conch. Svst., 

 vol. 2, p. 282. [Ety. none, belt] A 

 coiled shell, closely resembling a Helix, 

 having an open umbilicus; the sur- 

 face is transversely sculptured. Type 

 Z. algireus. 

 priscus, Carpenter, 1867, Quar. Jour. < too. 

 Soc., vol. 23, p. 331, and Acadian < tool., 

 p. 385, Coal Meas. 



CLASS CEPHALOPODA 



[Ety. kephale, head ; pons, foot.] 



The animals of this class are all marine, and they reach a higher state of an- 

 imal development than any other marine group among the Mollusca. Some of 

 them have a rudimentary, cartilaginous, cephalic skeleton, which indicates superi- 

 ority over other marine Mollusca. The locomotive organs consist of arms surround- 

 ing the head, furnished with sucking cups that take a firm hold on other objects. 

 Many have fins, and all can propel themselves by the forcible expulsion of water 

 from the respiratory chamber. They swim rapidly, creep on the bottom of the sea, 

 and are very predatory in their habits. The body is short, thick, and symmetrical, 

 with branchiae on both sides. 



The Palaeozoic fossils of this Class belong to the Order Tetrabranchiata (four- 

 gilled), which is represented in tropical seas by the Nautilus. The shells are 

 straight, as in the family Orthoceratidse ; curved, as in Cyrtoceratidse ; discoid, as in 

 the Gyroceratidse and Trocholitidse ; spiral, as in the Trochoceratidse ; involute, as 

 in the Nautilidae; or involute and having lobed sutures, as in the Goniatitidae. In- 

 ternally the shell is divided into numerous chambers by partitions, or septa, the 

 animal inhabiting the last chamber, and retaining connection through the preced- 

 ing chambers by a tube, or siphuncle, but having no connection with the interior 

 of the several chambers after having cut itself off by the secretion of the shelly 

 septa. The outlines of the septa are called sutures, and in Goniatites the eleva- 

 tions of the folded sutures are called saddles, and the intervening depressions lobes. 



