144 PEOCEEDIKGS OF THE MALACOLOGICAL SOCIETY. 



The heart and pericardium call for no comment. 



The gill, as already mentioned, is very large, for not merely does 

 it occupy the usual position on the dorsal wall of the mantle cavity, 

 hut it also, when the animal is fully extended, projects beyond the 

 mantle (PI. VIII, Fig. 1) as a prominent pectinate appendage. 



The Nervous System. — 'I'he nerve ganglia are well developed, and 

 closely massed round the oesophagus (PI. YIII, Figs. 6 and 7), 

 above which latter we find a pair of large, fairly closely approximated, 

 cerebral ganglia {e.g.), giving off nerves to the tentacles, and 

 supplying a pair of small buccal ganglia {l.g.) in front; ventrally 

 they give origin to a pair of delicate cerebro-pedal commissures, 

 which join with the great pedal ganglia. These last are situated 

 very close together, and each is divided into two (pd.g.), there being 

 in Adeorlis a small antero-ventral lobe from which the anterior pedal 

 nerves originate. This condition is highly suggestive of that seen in 

 many Naticoids (Haller [8], i.e. in N. lineata and in Sigaretus). The 

 pleural ganglia (pl.g.) are situated very close behind and below the 

 cerebral ganglia, with which they are practically fused ; each gives 

 off in front a pleuro-pedal commissure. From the left pleural a short 

 nerve is given off ; this dips down under the oesophagus, and almost 

 immediately enlarges into the sub-intestinal ganglion (s5.^.), which 

 extends back for a short distance under the oesophagus, but the 

 main mass of this ganglion remains on the left side of the middle 

 line ; from it a small commissure passes under the oesophagus round 

 its right side to join the right pleural ganglion. 



The supra-intestinal ganglion is also situated to the left of the 

 middle line ; it is innervated from the right pleural by a nerve which 

 crosses over the oesophagus, but it is also connected with the left 

 pleural by a still shorter nerve. Thus we see that the zygoneurous 

 condition is attained on both sides. But this zygoneury is a peculiar 

 one, on account of the shortness of the commissures, and is highly 

 suggestive of the condition seen in Lamellaria (Eouvier [10], pi. ix, 

 fig. 40), differing from that form mainly in the closer approximation 

 of the sub-intestinal ganglion to the left pleural ; in this latter 

 respect Adeorlis closely resembles Sigaretus, which is also doubly 

 zygoneurous (Haller [8], pi. xiii, fig. 1), only in the latter the 

 commissures connecting the supra-intestinal ganglion with the two 

 pleurals are very long. A comparison with the nervous system of 

 Rissoia (PL YIII, Figs. 8 and 9) shows a somewhat similar condition, 

 for here also there is a double zygoneury, but the sub-intestinal is 

 close to the left pleural, while the supra-intestinal is close to the 

 right pleural. 



The condition of the visceral loop attained in Adeorlis, JRissoia, 

 and Lamellaria suggests the culmination of the processes which 

 have been apparently going on within the ISTaticoid series ; we see 

 there a tendency to a shortening of the commissures connecting the 

 sub -intestinal with the right and left pleural ganglia, that on the left 

 side being shortest in Sigaretus, while in Crueihulum that on the 

 right is most contracted. All this tends to cause a great concentration 

 of the ganglia around the oesophagus, a condition attaining its 



