584 HISTORY OF SYSTEMS. 



ax^ritous structure of the animals of the microscopical multi- 

 locular shells bj M. Dujardin, in 1835;* and the third was 

 the confirmation of Cuvier's opinion regarding the non-para- 

 sitism of the cephalopod found in the shell of the Argonaute. 

 Hence, in 1836, we have, from the accomplished Professor 

 Owen, the following improved and excellent method of the 

 Cephalopoda i-j- — 



Order I. Tetrabranciiiata. Branchiae four in number. 

 The Nautilus pompilius is the type of the order. 

 Fam. 1. NAUTiLiD.ii;. Shell external; spiral or 

 straight ; septa smooth and simple, the last cham- 

 ber the largest, and containing the animal : siphon 

 central, or marginal and internal. — Ex. Nauti- 

 lus, Clymenes, Campulites, Lituites, Orthoceratites. 

 Fam. 2. Ammonitid^. Shell external ; spiral or 

 straight ; septa sinuous and with lobated margins, 

 the last chamber the largest and lodging the ani- 

 mal : siphon central, or marginal and external. — 

 Ex. Baculites, Hamites, Scaphites, Ammonites, 

 Turrulites. 

 Order II. Dibranchiata. Branchiae two in number. 



Tribe Decapoda. 



Fam. 1. Spirulid^. Shell partly internal ; cylindri- 

 cal, multilocular, discoid, the whorls separated ; 

 septa transverse, concave next the outlet, and with 

 regular intervals. Siphon marginal, and internal, 

 uninterrupted. Ex. Spirula. 



Fam. 2. Belemnitid^. Shell internal, composed of 

 an external calcareous sheath, formed by a succes- 

 sion of hollow cones, the exterior being the largest ; 

 of an internal horny sheath, also of a conical form ; 

 containing at its apex a chambered shell, the septa 

 of which are concave externally, and perforated by 

 a marginal and ventral siphon. Ex. Belemnites. 



Fam. 3. Sepiad^. Animal, body oblong, depressed, 

 with two narrow lateral fins extending its whole 

 length. Sliell internal, lodged in a sac in the back 

 part of the mantle, composed of an external cal- 

 careous apex or mucro, of a succession of calcareous 

 laminae with intervening spaces filled with air, and 

 supported by columns, but not perforated by a 

 siphon, and an internal horny layer, corresponding 



* See tlie Annales des Sciences Naturelles for 1834 and 1835. 

 t Cyclopaedia of Anatomy and Physiology. Part vi., May, 1836. 



