631 
Fig. 21, side view of a cast of a mould of this species. Fig. 22, a similar speci- 
men, but with nepionic stage and the beginning of the ananeanic substage in 
relief preserved in the centre, showing small umbilical perforation, subdorsan 
siphuncle (see also Fig. 23 for front view of same) and sutures. The sutures 
have slight ventral lobes in the ananeanic, but are almost if not quite straight on 
the venter of the paranepionic substage (shown in Fig. 23). The first suture 
was not visible in this specimen. 
Fig. 24 and 25. Ophidioceras tener, Barrande; Mus. Comp. Zodlogy, Schary 
Coll.; Loc., Bohemia. 3 diameters. Fig. 24, front view of section of neanic 
and ephebic volutions, the nepionic in relief in the centre. The outline of the 
ananepionic substage is given, but the cicatrix was unluckily destroyed by the 
incautious use of acid in cleaning it. The position of the siphuncle is nearer the 
venter than in older stages. Fig. 25, side view somewhat larger to show the con- 
strictions on the nepionic whorl and the great comparative size of the apical 
chamber and the first suture and constriction. 
Figs. 26-28. Ophidioceras tessellatum, Barrande; Mus. Comp. Zodlogy, Schary 
Coll. Fig. 26, X 3, to show dorsal outline of paranepionic volution without a 
dorsal furrow and ananeanic dorsum just below this with the beginning of con- 
tact furrow made by envelopment of the apex. Figs. 27 and 28, x 4 diameters, 
to show similar characters to those of O. ¢evzer, and, the matrix filling the umbili- 
cal perforation having been retained, this specimen shows also just how the 
paranepionic volution strikes the apex. The absence of an impressed zone is 
also noted in the paranepionic and position of siphuncle. 
Figs. 29-35. Ophidioceras rudens, Barrande; Loc., Bohemia; Mus. Comp. 
Zoblogy, Schary Coll. Fig. 29, natural size; Figs. 30 and 31, x 4 diameters; 
Figs. 32-35, natural size; Fig. 29, side view showing general form of this species 
and of the genus; Figs. 32-35 show the history of the contact furrow on free 
whorl with gibbous median dorsal face and lateral dorsal furrows or faces as in 
section 35, and also as on allof the close-coiled whorls. In the centre is the area 
of the spur, shown in section Fig. 34, and in the lower part is the modified con- 
tact furrow growing slightly narrower and shallower towards the aperture. Sec- 
tion of this part is given in Fig. 33; Figs. 30 and 31, side and front views of 
nepionic stage of another specimen showing cicatrix, form of ananepionic sub- 
stage, which is a compressed almost ‘quadragonal ellipse, metanepionic with 
venter broader than dorsum and paranepionic with dorsum broadening out more 
but still narrower than venter. 
Figs. 36-39. Lndolobus avonensis (sp. Dawson), Hyatt; Carboniferous; Loc., 
Joggins, Nova Scotia; Coll. L. Agassiz. Natural size. Fig. 36, side and front 
views showing the ana- and metanepionic substages in the centre (see also Fig. 
38, enlarged view, showing form more accurately and cicatrix). The ananeanic 
substage coming in when the apex is reached and the absence of the impressed 
zone until after this contact is shown above the apex in Fig. 37. Below this is 
seen the dorsal sutures and deep impressed zone produced by contact (shown also 
in Fig. 39, more enlarged). 
Figs. 40-42. Mimoceras (Gontatites) lituum, after Barrande, of. ci¢., Pl. x, 
showing the young and probably the adult of this form without any impressed 
zone and its similarity to some species of Nautiloidea, reduced one-third, 
