﻿60 BRITISH FOSSIL CEPHALOPODA. 



Genus Ascoceras, Barrande. 



1846. Cryptoceras, Barrande, ' Not. Prel. Syst. Sil. Boheme.' (Not D'Orbigny.) 



1847. Ascoceras, Barrande, ' Oesterr. Blatt. f. Litt.' &c, and ' Bull. Soc. Geol. de France,' 



2nd ser. vol. xii. 

 1865. Aphragmites, Barrande, ' Syst. Sil. de Boheme.' 

 — Glossoceras, Barrande, ' Syst. Sil. de Boheme ' [ = subgenus]. 



History. — The remarkable form so well known under the above generic title was 

 first discovered by Barrande in Bohemia. He regarded it as the most simple of the 

 Nautiloid Cephalopoda, and looked upon the portion of the body-chamber which lies 

 beside the distorted septa as a representative of the siphuncle. He hence compared 

 the genus to the Vaginati, and regarded it as more simple than they. At the same 

 time he recognised the existence of the small chambers below the body-chamber 

 with the mark of a siphuncle in the centre. The character of the siphuncle was 

 thus regarded as changing with age. The usual absence of any of the ordinary 

 septal portion of the shell has led palaeontologists to regard the part preserved as 

 the complete shell ; and the septa being seen on the side, the most extraordinary 

 definition has been given of the genus, such as " shell bent upon itself, as in Ptycho- 

 cerasT The so-called genus Aphragmites was founded for those shells which agreed 

 with Ascoceras in every particular, except that there were no sigmoid septa. Most 

 examples of Ascoceras show no peculiarity about the aperture, but in certain species 

 are found tongue-like projections on the dorsal side, corresponding to a sinus on the 

 ventral side, and for these the name Glossoceras has been proposed. The two genera 

 thus become representatives of the two series into which Barrande divides the 

 Nautiloids, — those with simple and those with contracted apertures. Seeing, however, 

 that the ventral sinus is present in Ascoceras, and in only some referred to Glossoceras 

 can any tongue-like process be found, it would appear that these forms are not 

 worthy of more than subgeneric distinction. As regards the name Cryptoceras, it 

 was the first proposed, but was afterwards rejected in favour of the present one. 



Description. — The true nature of the Ascoceras appears to have been completely 

 misunderstood. It is by no means the simplest form of Cephalopod, but the most 

 abnormal. Its interpretation may be best arrived at by a study of the beautiful 

 example figured by Barrande (' Syst. Sil. de Boheme,' vol. ii. PI. 51 3) and the surface 

 indications on English specimens. It is thus seen that the parts preserved do not 

 form two sets of septa, and two forms of siphuncle ; but that the curious sigmoid 

 septa are parts only of the others which are so constantly hidden. On examining 

 Barrande's section, it is seen that the hidden septa are separate from each other on 

 the side remote from the sigmoids, and join the siphuncle by well-marked necks. 

 The corresponding septa on the sigmoid side all pass by gentle and unbroken curves 



