﻿BEITISH FOSSIL CEPHALOPODA. 61 



into the single band which joins the hidden to the sigmoid portions ; but this band 

 examined on English specimens is found to be not really simple, but multiple, con- 

 sisting of several coalesced septa. In Barrande's figure there are four hidden septa 

 on the remote side ; but five are drawn on the nearer side to the sigmoids, which 

 latter are also four in number. Probably the fifth of the nearer septa is a mistake, 

 as it has no properly formed neck. Thus the number of the sigmoid lines corre- 

 sponds to that of the hidden septa, and affords a further proof of the correctness of 

 the present interpretation. The smaller parts of the septa do not appear to be lost 

 to view by falling off, as has been supposed, the caducous ones being of an ordinary 

 character, but they are hidden within the specimens, and are either not seen for 

 want of cutting, or, when the siphuncle is very near the side, are too obscure to be 

 observed. Another specimen figured by Barrande (PI. 93) shows this admirably ; 

 one side of it has the ordinary septal surface well exhibited, and the other, or cut 

 side, has the smaller hidden parts of the sigmoid septa very obviously run up into 

 one mass with a wide siphuncle. 



It is now, therefore, possible to describe Ascoceras in the ordinary way. The 

 earlier part is unknown, the body-chamber and the last few septal chambers only 

 being preserved in association. The section varies from elliptical to round. The 

 body-chamber is inflated, and gradually retracts to a neck-like prolongation, the 

 dorsal part of which is produced, and forms in some a tongue-like process (Glosso- 

 ceras). The ornaments are transverse, and consist either of ribs or of finer lines. 

 The earlier septa are of the ordinary kind, with very little convexity, and the 

 siphuncle excentric, in some of large size ; though its cavity may be more or less 

 obliterated by a later overgrowth of shell, and it appears to diminish rapidly in 

 size at last. The last few chambers are distorted, and their dorsal portions are 

 seldom seen : on the dorsal side of the siphuncle the septa are distinct as usual ; 

 but on the ventral side they soon coalesce into a single septum, and separate again 

 to form sigmoid partitions, encroaching on the side of the body-chamber. In some 

 examples these sigmoid portions of the septa are not developed {Aphragmites) . 



Subgenus G-lossoceeas. — The dorsal side is produced into a long tongue-shaped 

 process, almost dividing the aperture into two lateral portions ; the body-chamber is 

 very little inflated. 



Range. — This genus is confined to the Upper Silurian rocks, in which it has been 

 met with in England, Bohemia, and America. 



