244 
NAUTILOIDEA. 
Genus MESOCERAS, Barrande 
{Not rej^resented in the Collection.) 
Fig. 39. 
Mesoceras Bohemicum, Barr. — a, view of the straight side ; b, lateral view ; 
c, view of the convex side ; d, view of the apertiiral surface, oriented to 
correspond with h. Eeduced from Barrande’s figures. 
Gen. Char. Shell straight, short; transverse section elliptical. 
Aperture contracted, forming a large transverse orifice, rounded at 
both ends, with indications of a median lobe on the ventral (?) side of 
it (I, fig. 39, d). Siphuncle central. The bodj’-chamber only is known. 
Type (the only species known), M. Bohemicum, Barr. Silurian of 
Bohemia (Etage E, bande e 2). 
EemarJcs. The genus 31eosceras was founded by Barrande upon a 
fragment, consisting of the body-chamber of a shell resembling 
Gomphoceras in general form, but having a central siphuncle, and only 
obscure indications of a median lobe in the aperture. Barrande 
informs us that he kept this fossil in his cabinet twenty-five years 
before venturing to describe it, waiting in vain for the discovery of 
other specimens which would throw light upon it. 'WTth reference to 
the form of the aperture, he observes that there is a faint depression or 
interruption in the middle of the inferior border (I, fig. 39, c?), but that 
the state of preservation of the specimen (in black slate) does not 
permit of a conclusion being come to as to whether this depression 
has a natural or an artificial origin. If the former, it may have 
served as an exit for the respiratory funnel of the animal, as the 
smaller orifice in Gomphoceras is supposed to have done. An 
obscure median groove is also present, proceeding from the depres- 
sion, and there are transverse striae corresjeonding with it. All 
these phenomena, observes Barrande, tend to show that this is the 
ventral side of the shell. Mesoceras Bohemicum is compared by 
^ Syst. Sil. de la Boheme, vol. ii. 1877, Supplem. et Serie tardive, p. 198, 
pi. dviii. ; Hyatt, loc. cif. 
