EXPLANATION OF PLATES. 



Plate 1. Cerion incanum (Binney). 



Plate 2. Cerion casahlanccB Bartsch. 



Plate 3. Cerion uva (Linnaeus). 



Plate 4. Cerion crassilabris ("Shuttleworth" Sowerby). 



Plate 5. Cerion viaregis Bartsch. 



Fig. 1, plates 1-5. Central nervous system, posterior aspect. 



a. g. Abdominal ganglion. 



a. n. Abdominal nerve. 



b. c. Buccal commissure. 



b. g. Right buccal ganglion. 



b. V. Blood-vessel. 



c. b. V. Left cerebro-buccal commissure. 

 c. g. Bight cerebral ganglion. 



c. m. Cerebral commissure. 



c. pe. c. Right cerebro-pedal commissure. 



c. pi. c. Right cerebro-pleural commissure. 



Right cephalic retractor nerve. 



Left pleural ganglion. 



Mantle nerves. 



Right optic nerve. 



Pedal ganglion. 



Left pleural pedal commissure. 

 r. pi. g. Bight pleural ganglion. 

 r. u. iM. g. Right upper pleural ganglion. 

 " " Right sensory nerve. 



c. r. n. 

 1. pi. g. 



m. n. 



JJO. (6- 



pi. pe. c. 

 r. pi. g. 



Fig. 2, plates 1-5. Pallial organs from ventral side. 



a. Auricle. p. 



i. Intestine. u. 



k. Kidney. v. 



Fig. 3, plates 1-5. 



Right tentacular nerve. 



Pulmonary vein. 

 Ureter. 



Ventricle. 



Left branch. 

 Right branch. 



Anterior termination of buccal retractor muscle. 



r. r. Radular retractor. 



Fig. 4, plates 1-5. Genital system, from dorsal side. 



a. Atrium. 



a. g. Albumen gland. 



f. Flagellum. 



h. d. Hermaphroditic duct. 



h. g. Hermaphroditic gland. 



o. r. Ocular retractor. 



ov. d. Oviduct. 



Fig. 5, plates 1-5. Jaw. 

 Fig. 6, plates 1-5. Radula. 



1. 



4. 

 6. 



7. 



Rachidian tooth. 



let lateral tooth. 

 4th lateral tooth. 

 6th lateral tooth. 



7th lateral tooth. 



p. 



r. m. 

 B.p. 

 8p. d. 



V. 



v.d. 

 V. r. 



10. 

 12. 

 13. 



16. 

 18. 



Penis. 



Penis retractor muscle. 



Spermatheca. 



Spermatic duct. 



Vagina. 



Vas deferens. 



Vaginal retractor. 



10th marginal tooth. 

 12th marginal tooth. 

 13th marginal tooth. 

 16th marginal tooth. 

 18th marginal tooth. 



Plate 6. Cerion incanum (Binney) and Cerion viaregis Bartsch. 



Fig. 1. Alimentary tract of Cer^ow^ncan^im from dorsal side. 



Fig. 2. Musculature of Cerion incanunij uncoiled. 



Fig. 3. Atrium of Cerion incanum, opened to show fleshy protuberance and fleshy ribs. 



Fig. 4. Side view of central nervous system of Cerion viaregis. 



Ocular retractors. 



Penis. 



Right pleuro-pedal commissure. 



Right pedal nerves. 



Right cephalic retractor. 



Right pedal ganglion. 



Right pleural ganglion. 



Salivary ducts. 



Salivary gland. 



Right sensory nerve. 



Stomach. 



Right tentacular nerve. 



Tentacular retractors. 

 . . _ . Vaginal retractor. 



u. r. pi. g. Upper right pleural ganglion. 



Vagina. 



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