PLATE II. 



Fitr. 21. 



Fig. 22. 



Fig. 23. 

 Fig. 24. 

 Fig. 25. 



Fis. 26. 



Fig. 59—6 



Fig. 64 



Fig. 65 



Fig. 66, 



Fig. 67 



Fig. 68 



Fig. 69 



Fig. 70, 



Fig. 71 



Fig. 72 



Fig. 73 



Fig. 74 



Fig. 75 



Fig. 76 



Fig. 77 



Fig. 78 



Fig. 79. 



Central nervous system Clio (Creseis) aciaila (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; ot 



and oi , left and right otocyst. 

 Central nervous system Clio pyrainidata (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 columnella (Rang), from the right side. 

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



glands; c, vas deferens. 

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

 /, pedal ganglion; v, 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. Different shells of Cavolinia (Diacria) trispinosa (Les.). 2 X. 



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

 The same, seen from the left. 2 • . 



Probably anomalous shell of Cavoliuid gibbosa (Rang). 2 X. 

 The same, seen from the left. 2 ■ . 

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



tridentata (Forsk.). Seen from the right. 2 ■ . 

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

 58. Series of shells of Cavolinia inflcxa (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 coinprcssd" Souleyet. Ventral view. 10 •. 

 Shell of "Cleodora pjgniafa" Boas. 



Shell of '^Pleiiropus longifilis" Troschel, from Naples. Dorsal view. 10 ■:. 

 Same specimen, seen from the right. 10 . 



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

 Same specimen, seen from the left. 10 ■ . 

 Shell of '^ Hyalaca rotnndata\ Dorsal view. 10 X. 

 The same specimen, seen from the right. 10 ■'. 

 Shell of '^ Hyalaca Icvigata" . Dorsal view. 10 • . 

 Same specimen, from the right. 10 • . 

 Shell of "Hyalaea dcprcssa". Dorsal view. 10 <. 

 Same specimen, from the right. Nearly aiiult; the shell is alread}' very much like tliat of 



Cavolinia inflexa. 

 Shell of "■ Hyalaea dcprcssa". 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. 

 Explanation of letters the same as in fig. 78. Besides, c, cerebral ganglion; 6, tentacular nerve. 



