278 GILBERT C. BOURNE. 



left. But beyond this distortion Avliich it shares with the 

 other organs of this region, the nervous system presents few 

 features requiring special description. The otoliths lie a 

 short distance behind the pedal ganglia, and are connected 

 with the latter by short nerves. The two stout nerves 

 passing from the pedal ganglia, that from the right ganglion 

 distributed to the upper and. that from the left ganglion 

 distributed to the lower surface of the byssus muscle are 

 worthy of mention, because de Lacaze Duthiers (8) describes 

 a large nerve passing from the visceral ganglia to the 

 byssus muscle in Anomia. No such nerve is present in 

 ^Enigma, the byssus muscle being wholly innervated from 

 the pedal ganglia. The branchial and pallia! nerves issuing 

 from the right and left visceral ganglia should be noted. 

 Tlie branchial nerve of either side runs straight down into 

 the suspensory fold of the gill axis, and there enters a 

 distinct branchial ganglion (fig. 3, hr.g.), from which fine 

 nerves run forwards and backwards in the gill axis. The 

 pallial nerve issues separately from the branchial nerve on the 

 right side, but the two have a common origin from the left 

 visceral ganglion. The branches of the two viscero-pallial 

 nerves diverge in the mantle lobes and unite in each mantle 

 lobe with a distinct circumpallial nerve, which forms a 

 complete ring in the thickened margiii of the mantle, and 

 forms a connection anteriorly with nerves issuing from the 

 cerebro-pleural ganglia. 



Histology. — The specimens of Enigma collected by 

 Mr. Shelford were so well preserved that I have been able 

 to work out the histology of some of the organs in some 

 detail, but I do not propose here to do more than give an 

 account of some of the more striking features that came 

 under my notice. A detailed account of the histology of 

 various members of the Lamcllibranchia, including the 

 Anomiacea, is indeed a desideratum, but for such a task 

 fresh specimens ai-e necessary, and where they are not avail- 

 able it is inexpedient to attempt more than a description of 

 such characters as cau be accurately studied in sections. 



