dur. Ne@ericus. 
Vou. 1x. FEBRUARY, 1896. No. 10 
THE AULACOPODA: A PRIMARY DIVISION OF THE MONOTREMATE 
LAND PULMONATA. 
BY HENRY A. PILSBRY. 
If the foot of a living or properly preserved Helix or Polygyra 
be compared with that of a Zonites, Pyramidula (Patula) or Ario- 
imax, a conspicuous point of difference becomes apparent. In the 
latter three genera a groove or furrow may be seen running the 
whole length of the foot, a short distance above and parallel to its 
edges; while no such structure is present in the first named genera. 
These furrows are the pedal grooves. ‘They rise slightly at the 
tail, and meet above it; and at this point there is often a local 
deepening of the groove, and a greater development of the mucus- 
secreting cells lining it. This is the “caudal mucus pore,” conspic- 
uous in Zonites, Ariolimax, ete. There is vast variation in the 
degree of development of this pore,—from a barely visible widening 
of the united pedal grooves, to a deep slit or a triangular pit sur- 
mounted by a fleshy horn; and in some forms it is extremely difficult 
to say whether a pore exists or not, so nicely graduated are the stages 
of its development. Consequently, we find genera very closely 
allied in other characters, differing in this one. Such are Pecilo- 
zonites, without pore, G'astrodonta with it; Ariolimax with pore, 
Prophysaon without it; and many similar cases.’ In spite of all the 
instances of this kind, the tail pore has been a great bugaboo to the 
systematists, while the pedal grooves, of which this pore is merely an 
1 Compare also, in this connection, Cockerell’s remarks in Journal of Malacol- 
ogy (The Conchologist), Vol. ii, p. 118. 
