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lobed and indented at the circumference; tube or syphon marginal, not 

 piercing the septa. 

 A fossil. 



Turrilites. Shell spiral, turreted, multilocular; the whorls contiguous, 

 and whole apparent; the partitions articulated by sinuous sutures; septa trans- 

 verse, lobed and indented at the circumference; aperture rounded. 



A fossil. 



Bacculites. Shell straight, cylindrical, sometimes rather compressed, 

 slightly conical; the partitions articulated by sinuous sutures; septa trans- 

 verse, a little distant; the disc imperforated, lobed and indented at the cir- 

 cumference. 



A fossil. 



DIVISION II. MONOTHALAMOUS CEPHALOPODA. 



Shell unilocular, icholly external, and enveloping the animal. 



Argonauta. Shell univalve, unilocular, involute, very thin; spire bicar- 

 inated, tubercular, turning into the aperture. 



A. argo, A. tuberculata, A. nitida. 



DIVISION III. NAKED CEPHALOPODA.— Four Genera. 



JVb shell either internal or external. A solid, free, cretaceous or horny 

 substance is found in the inside of most of these animals. 



Octopus. No internal solid substance. 

 A molluscous animal. Sepia Octopus, Linn. 



Loligopsis. No internal solid substance. 

 A molluscous animal. 



Loligo. An elongated, thin, transparent and horny lamina, inclosed in 

 the interior of the body, near the back. 

 A molluscous animal. Sepia Loligo, Linn. 



