﻿88 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 102 



anteriorly to supply the proboscis, the labial region, and the muscular 

 elements of the buccal mass. The innermost nerve runs to the anterior 

 region of the buccal mass, turns posteriorly, and runs back to join the 

 buccal ganglia at the posterior end of the buccal mass. 



Each cerebral ganglion gives rise ventrally to a stout commissure, 

 which descends to the pedal ganglion below it. At a point on the 

 pedal ganglion, just posterior to the entrance of the cerebro-pedal 

 commissure, another large commissure enters from the pleural 

 ganglion. 



The pedal ganglia are larger than the cerebral ganglia and, in 

 Thiara, are strikingly different from those in the Amnicolidae in 

 being laterally rather than dorsoventrally compressed. They are 

 closely connected at their inner surfaces and do not have what might 

 be called a commissure. The ventral ends of these ganglia each give 

 rise to two stout pedal nerves. Smaller offshoots of varying size may 

 be present. 



The statocysts are rather prominent in this species and are located 

 on the upper ventral surface of each pedal ganglion. No prominent 

 nerve running from the statocyst to the cerebral ganglion was ob- 

 served, although there is one in Paludomus (Seshaiya, 1934), Thiara 

 (Thiara) amarula^ Thiara (Melanoides) tuherculata, and Thiara 

 (Melanoides) costata (Bouvier, 1887). However, a rather prominent 

 nerve is found descending ventrally from the statocyst. Each stato- 

 cyst contains a single calcareous, disc-shaped statolith or otolith. 

 Other members of the genus Thiara possess a similar otolith, but 

 those of Paludomus (Seshaiya, 1934), Nassopsis, and Bythoceros 

 (Moore, 1889) contain numerous small otocones. 



The pleural ganglia are round and bulbous and closely appressed 

 to the ventral and posterior end of the cerebral ganglia. They are 

 connected to the latter by short commissures. The right pleural 

 ganglion gives rise to the rather large supraintestinal nerve and the 

 right pallial nerve. The former nerve joins the small supraintestinal 

 ganglion on the left side of the body. The left pleural ganglion gives 

 off on its left side a small nerve, which passes up to the left side of 

 the mantle region. Just behind this ganglion is the equally large, 

 oval, subintestinal ganglion. At its juncture with the pleural ganglion 

 another thin nerve arises to the left and ascends toward the mantle. 



The posterior end of the subintestinal ganglion gives rise to two 

 prominent nerves: (1) A pallial nerve, which first makes a short, 

 complete loop and then passes across the back of the animal to the 

 right side, where it is joined by a similar nerve from the right pleural 

 ganglion; and (2) the right visceral nerve, which proceeds posteriorly 

 to join the small obscure visceral ganglion. 



