218 
NAT7TIL0IDEA. 
half apart : greatest width of last chamber (at septum) two inches 
three lines, length of last chamber two inches four and a half 
lines. 
“ There are clearly two species confounded by Sowerby in the 
Sil. Syst. under the name Orihoceras pyriforme ; the difference in 
form he supposed to be produced by the direction of pressure, but 
I find it to be constant in perfectly uncrushed specimens. To that 
represented by his upper figure I would restrict his specific name 
pyriforme r .... {JSrCoy.) 
Remarhs. To the present species I have referred an imperfect 
specimen in which the larger orifice is remarkably short transversely, 
agreeing in this and in other respects with Sowerby’s type, as figured 
by Blake. 
Horizon. Lower Ludlow. £tage E ( = Salopian). 
Localities. British. Herefordshire. — Foreign. Lochkow, Kosofz, 
Wiskocilka, Bohemia. 
Eepresented by a single British example and a few Bohemian 
ones. 
Gomphoceras Agassizi^ Barrande. 
1847. Gomphoceras Ayassizi, Barrande, Haidinger, Berichte fiber die 
Mittheil. von Freund, d. Naturwiss. in ’\^’ien, Band iii. p. 269. 
1867. Gomphoceras Ayassizi, Barrande, Syst. Sil. de la Boheme, vol. ii. 
pt. i. p. 269, pi. Ixxxviii. ff. 1-8. 
Bp. Char. The shell presents the usual convexity on the ventral 
side, while on the dorsal it is nearly straight. The transverse 
section is almost circular, in specimens which have not been sub- 
jected to compression. The body-chamber is flattened in a direction 
parallel to the longer diameter of the large orifice of the aperture. 
This flattening gives a very distinctly subtriangular form to this 
region. The body-chamber occupies at least half of the total length 
of the shell, and its capacity exceeds that of the septate part of the 
latter. The aperture is nearly parallel to the plane of the last 
septum ; the larger orifice is very wide and has the form of an 
ellipse of which the two axes are in the ratio of 1 : 2. Its greatest 
width equals | of the diameter of the body-chamber ; its dorsal 
border is almost straight or but very slightly sinuous in the centre. 
The channel uniting the larger with the smaller orifice is extremely 
short ; the latter is circular, and its borders project slightly above 
the surface of the body-chamber. The distance between the septa 
does not exceed ^ the diameter of the shell. Their convexity 
amounts to of that diameter. The siphuncle is situated in the 
median line about midway between the dorsal margin and the 
