198 LAND AND FRESHWATER 
The sutural tube in this species opens internally, a short distance 
from the peristome, by a small longitudinal slit, and then passes 
outside the suture to the aperture, where it is deflected upwards, and 
runs vertically for 2 or 3 millimetres on the exterior of the penulti- 
mate whorl, opening to the air at the extremity. I found this tube 
to be partly lined by a perforated process of the mantle, communicating 
internally, by means of a passage beneath the shell-muscle, with a 
very small orifice inside the air-chamber in the neck of the animal, 
and thus affording free access of the air to the pulmonary cavity, 
even when the mouth of the shell is hermetically closed by the 
operculum. The existence of this conformation cannot easily be 
observed during life*, on account of the manner in which the mantle 
lines the interior of the shell; but after killing the animal in hot 
water, and extracting it from the shell, the little free perforated 
process is distinctly seen, and is then about 2 millim. in length, its 
dimensions having been, doubtless, much contracted by the hot water. 
“The genus Spiraculum of Pearson was established upon the species 
S. hispidum, P. By Dr. Pfeiffer that species has been referred to 
Pterocyclos, to which it is certainly nearly allied, although there 
appear to be good reasons for its generic separation. I have never 
had an opportunity of examining the animal of S. hispidum; but 
in the autumn of 1861 I met with a second species of the same 
genus in the neighbourhood of Ava (S. avanwm, mihi). This species 
is furnished with a small tube similar to that in S. hispidum, open- 
ing at both ends, internally inside the body-whorl, close to the 
suture and at a short distance behind the peristome, and externally 
into the air, the short tube on the exterior of the whorl being free 
and curved backwards. The individual which I examined was just 
adult ; there was no tubular process of the animal, but it was re- 
placed by a deep notch in the mantle corresponding to the perforation 
of the shell. It is possible that, in older specimens, this notch may 
become altered into a more or less perfect tube; but, as the specimen 
examined was full-grown, this is scarcely probable. 
“The other tube-bearing genera with open tubes are Streptaulus, 
which can scarcely be considered as generically distinct from 
Raphaulus, and Opisthoporus. I have not been able to examine the 
animals of either of these. The tube in the aberrant genus Alycceus 
opens anteriorly into the body-whorl by a longitudinal slit, as in the 
other genera; but after running back along the exterior of the 
suture for a greater or less distance, corresponding with the inflated 
portion of the last whorl, it is closed at the posterior termination, 
I have seen the soft parts of several species, including the compara- 
tively large A. wmbonalis, Bens., but have been unable to detect any 
organization corresponding to the shelly tube. 
It was long since observed by Mr. Benson that no portion of the 
animal of Pterocyclos appeared to correspond with the peculiar 
* “This is doubtless the reason that the tubular process of the mantle was 
overlooked by so careful an observer as Mr. Benson, who, I believe, confined 
his observations to the living animal. (See Ann. & Mag. Nat. Hist. ser 
vol. iy. p. 94.)” 
