248 
NATJTILOIDEA. 
of the shell ; its ornaments may consist of transverse lines or of 
annnlations, and these two descriptions of markings have been 
employed by Barrande to separate the species into two groups. 
Ascoceras occurs in the Ordovician of Xorth America and the 
Silurian of Europe, by far the greater proportion of the species 
coming from Bohemia ; thus, fifteen species have been described by 
Barrande in the last-named country, three in Canada by Billings, 
and three in England by Salter and Blake. 
Uemarlcs. Barrande’s opinion that Ascoceras offered a more simple 
type of structure than that of Orilioceras has been confuted by 
Blake, who has very clearly described the structure of the former 
genus, showing that instead of being one of the most simple among 
the Nautiloid Cephalopoda, the shell of Ascoceras is really the most 
abnormal. 
Barrande’s suggestion that the body-chamber of Ascoceras is 
analogous with the large marginal siphuncle in Endoceras was 
based upon the assumption that the siphuncle changed with age, 
commencing with a comparatively small tubular siphuncle (fig. 42, 
si) and expanding into a large cavity, whose capacity was, however, 
reduced by the distorted septa formed on one side of it. It may 
well be suiDposed, however, that the whole of the cavity posterior to 
the last-formed (arched) septum contained that portion of the 
animal’s body answering to the visceral cone ^ of Endoceras 
Ascoceras Barrandei, Salter. 
1858. Ascoceras Barrandii, Salter, Quart. Journ. Geol. Soc. vol. xiv. 
p. 180, pi. xii. f. 7. 
1859. Ascoceras Barrandei, Salter, in Murchison’s ^ Siluria,’ 3rd ed. 
p. 259, Foss. Gr. 62. 
1867. Ascoceras Barrandei, Barrande, Syst. Sil. de la Boheme, vol. ii. 
pt. i. p. 335. 
1882. Ascoceras Barrandei, Blake, British Foss. Ceph. pt. i. p. 207, 
pi. xxvi. f. 9. 
Bp. Char. The type species, which is contained in the Museum of 
Practical Geology, is thus described by Blake : — “ Section at the base 
Which secreted the calcareous “sheath” (see fig. 13, p. 131). 
^ I will take this opportunity of supplying a deficiency in the description of 
Endoceras (p. 129), in which I omitted to mention the body-chamber. This is 
known only by fragments representing its posterior portion, in two species 
described by Barrande, viz . : — Endoceras conqiiassatum, and E. novator (Syst. 
Sil. de la Boheme, vol. ii. Texte iii. 1874, pp. 675, 676, plates ccxlvii. and 
ccccxv.). 
