EXPLANATION OF PLATES. 



Plate 1. Cerion incanum (Binney). 



Plate 2. Cerion casablancoe 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. c. Left cerebro-buccal commissure. 

 c. g. Right cerebral ganglion. 



c. m. Cerebral commissure. 



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



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



c. r. n. Right cephalic retractor nerve . 



1. pi. g. Left pleural ganglion. 



m. n. Mantle nerves. 



o. n. Right optic nerve. 



pe. g. Pedal ganglion. 



pi. pe. 0. Left pleural pedal commissure. 



r. pi. g. Right pleural ganglion. 



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



8. n. Right sensory nerve. 



t. n. Right tentacular nerve. 



Pallial organs from ventral side. 



p. V, 



Pulmonary vein. 



Ureter. 



Ventricle. 



Fig. 2, plates 1-5. 



a. Auricle. 



i. Intestine, 



k. Kidney. 



Fig. 3, plates 1-5. Anterior termination of buccal retractor muscle. 



1. Left branch. r, r. 



r. Right branch. 



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. 

 Fig. 6, plates 1-5. 



Jaw. 

 Radula. 



Rachidian tooth. 

 1st lateral tooth. 

 4th lateral tooth. 

 6th lateral tooth. 

 7th lateral tooth. 



10. 

 12. 

 13. 

 16. 



18. 



Radular retractor. 



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 Cerion mcanwrn from dorsal side. 



Fig. 2. Musculature of Cerion incanum, 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 cephaUc retractor. 

 Right pedal ganglion. 

 Right pleural ganglion. 

 Salivary ducts. 

 Salivary gland. 

 Right sensory nerve. 

 Stomach. 



Right tentacular nerve. 

 Tentacular retractors. 

 Vaginal retractor. 

 pi. g. Upper right pleural ganglion. 

 Vagina. 



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