PLATE IL 



Fig. 



!I. 



Fig. 22. 



Fig. 23. 

 Fig. 24. 

 Fig. 25. 



Fig. 26. 



Fis 



Fig. 59—6 



Fig. 79. 



Central nervous system Clio (Crescis) acicula (Rang). Ventral view. 



/ and /', left and right pedal ganglion; v and v' , left and right visceral ganglion; i and i', 



nerves to the fins; 2, left pallial nerve; 3, right pallial nerve; 4 and 5, visceral nerves; et 



and ot' , left and right otocyst. 

 Central nervous system Clio pyrauiidata (Linn.). Ventral view. 

 Explanation of letters the same as in fig. 21. Besides, 6, tentacular nerve. 

 Buccal ganglia Clio pyraniidata (Linn.), fused together as in all Cavoliniidae. 

 Cervical organ Cuvierina coluinnella (Rang), from the right side. 

 Genital organs of the same, dorsal view. g, gonad; a, its efferent duet; /;, accessory genital 



glands ; c, vas deferens. 

 Central nervous system of the same. A, ventral view. B, from the left side. 

 p, pedal ganglion; %', visceral ganglion; c, cerebral ganglion; a, anterior pedal commissure. 



I and 2, nerves to the fins; 3, left pallial nerve; 4, right pallial nerve; 5 and 6, visceral 



nerves; 7, a nerve perhaps supplying the cervical organ; 8 and 9, nerves to the tentacles 



and to the lips; ot, otocyst. 

 31. Difierent shells of Cavoliiiia (Diacria) trispinosa (Les.). 2 X- 



^Hyalaea affinis", a variety of Cavolinia tridentata (Forskal); dorsal view. 2 X. 

 The same, seen from the left. 2 • . 



Probably anomalous shell of Cavolinia gibhosa (Rang). 2 X. 

 The same, seen from the left. 2 ;■; . 

 44. Series of shells of '^ Plcuropiis longifilis" Troschel, to show the transition to the adult Cavolinia 



tridentata (Forsk.). Seen from the right. 2 X- 

 53. Series of the same specimens, dorsal view. 2 y. 

 58. Series of shells of Cavolinia inflexa (Les.), transition from the variety lata to longa. Dorsal 



view. 2 >; . 

 Series of the same specimens, seen from the left. 2 /,. The specimens i and 4 in these 



series were caught by the Siboga, the other specimens are from the Atlantic. 

 Shell and animal of "'Cleodora coniprcssa" Souleyet. Ventral view. 10 • . 

 Shell of " Clcodora pygmaea" Boas. 



Shell of '^ Pleuropus longifilis" Troschel, from Naples. Dorsal view. 10 X. 

 Same specimen, seen from the right. 10 '•■■'. 



Shell and animal of '^ Fleuropns longifilis" Troschel. (Siboga-specimen). Dorsal view. 10 X. 

 Same specimen, seen from the left. lo • . 

 Shell of '^ Hyalaea rotundatd' . Dorsal view. lo X. 

 The same specimen, seen from the right. 10 X. 

 Shell of ^Hyalaea Icvigata" . Dorsal view. 10 X. 

 Same specimen, from the right. 10 •'. 

 Shell of "Hyalaea depressa". Dorsal view. 10 x. 

 Same specimen, from the right. Nearly adult; the shell is already very much likc that of 



Cavolinia inflexa. 

 Shell of '^Hyalaea depressa". Dorsal view. 10 :• . A younger stage than the foregoing one. 

 Same specimen, from the right. 10 . 



Central nervous system of Cavolinia tridentata. Ventral view. 

 p, pedal ganglion; v, visceral ganglion; i, nerve to the fins; 4, left pallial nerve; 3, right 



pallial nerve; 2 and 5, visceral nerves; ot, otocyst. 

 Central nervous system of the same, seen from the left. 

 E.xplanation of letters the same as in fig. 78. Besides, e, cerebral ganglion; 6, tentacular nerve. 



