PROSOBRANCH GENUS PONTIOLTHAUMA. 459 
being so disposed as to form a slight spiral gutter. The succeeding 
segment of the cesophagus (Oe.), which is separated from the 
pharyngeal bulb by an exceedingly deep cleft, is very thick- 
walled and somewhat laterally compressed ; its interior is longi- 
tudinally plicated, but the plice are not so fine as are those of 
the pharyngeal buib, and they become coarser towards the 
stomach. The stomach is expanded, and its inner wall shows 
several prominent longitudinal folds. The disposition of the 
ducts of the digestive gland appears to be similar to the condition 
met with in P. abyssicola (Pl. 42. fig. 11), aud, as in that species, 
the intestine narrows considerably. 
A well-developed Leiblein’s gland of the typical “ poison-gland ” 
type is present. The gland itself and the mass of its much- 
convoluted duct lie to the sight side of the esophagus; but a 
noteworthy detail regarding this structure is that the duct enters 
the pharyngeal bulb upon its ventral face (Pl. 42. fig. 4, L.Gl.), 
whilst in the majority of Prosobranchs the cesophageal diverti- 
culum appears to arise dorsally. 
A pair of small salivary glands are associated with the minute . 
radula-sae (Pl. 42. fig. 4, R.S.). They are compact and have a 
sharply recurved, narrow, distal prolongation such as occurs in 
P. abyssicola (Pl. 42. fig. 18, 8.Gl.). 
The radula consisted of 23 rows of the formula 1—O—1. The 
teeth (Pl. 42. figs. 5-9) are typically Toxoglossate; they are hollow, 
with subterminal external openings and have barbed extremities. 
The nervous system having been torn before the speciinen 
reached me, it is not practicable to give a satisfactory account of 
its characters. The cerebral ganglia, which occupy the normal 
position, are hardly at all separated from each other; while the 
pedal ganglia are situated towards the right side of the introvert 
sheath, and the cerebro-pedal connectives are exceptionally long 
and delicate. 
PonTIOTHAUMA ABYSSICOLA, E. A. Smith. (PI. 42. figs. 10-14.) 
When describing this species Smith expressed some doubt as 
to the closeness of its affinity with P. mirabile ; and the structure 
of the soft parts will certainly justify the removal of P. abyssicola 
from the genus Pontiothawma. Since, however, so little is yet 
known of the anatomy of other Pleurotomoids, it will perhaps 
be advisable to wait until further details are published regarding 
Pleurotomeila, &c., before proposing another new sectional name 
for Pontiothauna abyssicola. 
