CEPHALOPODA. I!) 



of eight arms, and two additional elongated tcntacula. In this tribe the suckers are 

 armed, and the mantle supports two lateral or terminal fins. The " Octopoda" were 

 divided into two families, termed " Nuda" and " Testacea" according to the absence or 

 presence of an external shell. In the second family was placed Better ophon, an extinct 

 genus proposed by De Montfort for remains peculiar to the Palaeozoic series, which 

 Defrance had associated with Argonaut, but which subsequently had been considered 

 as belonging to a heteropodous mollusc. The reasons which induced Professor 

 Owen to restore Bcllerojjhon to a place among the Cephalopods are not stated. If 

 however, its remains belong to this class, they present the anomaly of the testaceous 

 Octopods having been without a representative from the end of the carboniferous 

 epoch until the deposit of the newer tertiary formations, when the family reappears in 

 the genus Argonaut. The decapodous Cephalopods were divided into four families, 

 according to the position of the fins, the nature of the internal shell, and the condition 

 of the infundibular cartilage. The ordinal and sub-ordinal distinctions of Professor 

 Owen have been adopted by M. Deshayes, but that naturalist has subdivided the 

 Octopoda and Decapoda each into two groups ; the Octopoda according to their 

 possessing one or two rows of suckers, and the Decapoda according to the position of 

 the fins. These characters appear to be of secondary importance, and, by themselves, 

 can scarcely be considered as sufficient for more than generic distinctions. M. 

 d'Orbigny has availed himself of the presence of suckers and tentacles, characters 

 originally proposed by himself and M. Ferussac as ordinal distinctions, and accordingly 

 the Cephalopoda are divided by him into Acetabulifera and Teiitaculifera. The sub- 

 ordinal distinctions of Professor Owen are adopted by this author ; but in his subdivision 

 of Octopoda he has drawn his characters from the presence or absence of the apparatus 

 for resistance, and the aquiferous pores. The Decapoda are arranged by him in two 

 groups, according to the modification in the structure of their eyes, to which I have 

 before alluded. The first group (Ifgopsidte) is divided into three families. In two of 

 these, Sepida and Loligida, the characters are taken from the retractile power of the 

 tentacular arms, the condition of the internal shell, and the presence or absence of an 

 eyelid of a part of the auditory apparatus called by him the auricular crests (cretes 

 auriculaires), and of a superior ligament to the funnel ; the character of the third 

 family (Spirulida) rests entirely on the internal shell. The second group (Oigopsida) 

 also consists of three families, two of which, Zoligopsidce and Teuthida, depend on the 

 presence or absence of a lachrymal sinus and the auricular crests, on the funnel being 

 or not being provided with an internal valve and ligaments, on the condition of the 

 aquiferous pores, and on the shell being with or without air-chambers. The Belem- 

 nitidce, the third family, is separated entirely by the character of the internal shell. 



The peculiar modifications in the structure of the eyes among the decapodous 

 Cephalopods appear to be of sufficient importance to justify the subdivision of that 

 sub-order into the two groups proposed by M. d'Orbigny ; and inasmuch as the adoption 



