REPORT ON THE CEPHALOPODA. 



123 



Subfamily Eusepii, Steenstrup. 

 Sepia, Linne. 



Oue of the most marked accessions of new species lias been to this already large 

 genus, which has been augmented to the extent of no less than ten new types as the 

 result of the Challenger Expedition. It is noteworthy, moreover, that all these were 

 obtained between Port Jackson, Australia, and Japan, a fact which wUl be again 

 alluded to when treating of distribution (see p. 222). 



The species of this genus being very numerous and differing only in minute, though 

 to all appearance constant characters, it has been necessary to enter into considerable 

 detail in their descriptions, and the more so, inasmuch as the accounts of nearly all the 

 earlier writers have left much to be desired in this respect. This is the case especially 

 with respect to the shell or sepiostaire, regarding the different parts of which no settled 

 terminology seems to have been adopted, even by those writers who have most clearly 

 recognised its systematic importance. I have therefore found it necessarj'- to adopt a 

 series of names for descriptive purposes, and have endeavoured to select those which 

 should be convenient, readily suggestive of the 

 structures to which they refer, and devoid of any 

 abstract morphological significance with regard to 

 their origin or homology. The annexed woodcut 

 shows the names chosen, with respect to one or two of 

 which it may be advisable to make some observations. 



The last loculus is a term borrowed from 

 d'Orbigny, who adopted it for the most recently 

 deposited calcareous layer ; the proportion which it 

 bears to the area of the shell is very characteristic, 

 and appears to be constant within certain limits. 

 Professor Steenstrup informs me that it varies 

 according to the season of the year. This relation 

 is for practical purposes most conveniently expressed 

 by dividing the total length of the shell into one 

 hundred parts, and stating how many of them are 

 occupied by it ; this quantity I propose to designate 

 briefly as the "locular index." 



The hinder generally hollow ventral surface of the shell I have called the " striated 

 area"; valuable characters are derived from the curvature of the parallel lines formed 

 by the margins of the loculi. 



In most shells a thin fillet of calcareous matter runs along either side of this area. 



Fig. 4. — Shell of Sepia mestus, Gray, showing the 

 terms used in describing different parts of it. 

 cm., chitinous margin; i.e., inner cone; l.i.c, 

 limbs of the inner cone; 1,1., \s.s,t loculus; s.a., 

 striated area ; sp., spine. 



