G. A. DREW ON YOLDIA LIMATULA, SAY. 35 



EXPLANATION OF FIGURES. 



Fig. 1. Expanded adult specimen, seen from the right side. 



Fig. 2. Left shell-valve, seen obliquely from the dorsal margin. 



Fig. 3. Adult specimen represented as seen from the right side, with the right 

 shell-valve and mantle-lobe removed. The siphons are shown cut longitudinally. 



Fig. 4. Same as the above with the right palp and gill removed, figured to show 

 the relations of internal organs. The nerves leaving the ganglia are shown only on 

 the left side. (Partially reconstructed.) 



Fig. 5. Specimen about 1 mm. long. Represented as a partially transparent 

 object, seen from the right side, after the right shell-valve and mantle-lobe have been 

 removed. (Partially reconstructed.) 



Fig. 6. Tip of a retracted siphonal tentacle. 



Fig. 7. Portion of an extended siphonal tentacle, with a swelling caused by the 

 pressure of the blood, seen as a transparent object. 



Fig. 8. Transverse section of a siphonal tentacle. 



Fig. 9. Anterior portion of the shell, and the reflected margins of the foot, just 

 before they are brought together and withdrawn into the shell. 



Fig. 10. An animal as it appears while feeding. 



Fig. 11. Posterior portion of a specimen about .5 mm. long. 



Fig. 12. Transverse section of a specimen about 1 mm. long, showing the thicken- 

 ing of the ridges leading to the base of the siphons, and the pushing in of the ventral 

 wall of the exhalent siphon. Taken near the base of the siphons. 



Fig. 13. Posterior portion of a specimen about 2 mm. long. 



Fig. 14. Transverse section of a specimen about 1 cm. long, taken through the 

 bases of the siphons. One of the ridges is shown joining the inhalent siphon. The 

 section also includes a portion of the wall attaching the exhalent siphon to the 

 dorsal portion of the mantle. 



Fig. 15. End of the exhalent siphon of a specimen .7 mm. in length. 



Fig. 16. Projection of the margin of the mantle opposite the extremity of stripe 



on the anterior end of the shell. 



Fig. 17. Section of the anterior projection of the margin of the mantle. 



Fig. 18. Transverse section of a palp-appendage. 



Fig. 19. A pair of gill plates seen from their anterior surfaces. The suspensory 

 membrane, the walls of the plates joining the plates next in succession, the longitudi- 

 nal muscles, and the bases of the chitinous rods are shown in section. These are all 

 cut across in separating the pair of plates from the pair lying in front. (Drawn from 

 a study of sections.) 



Fig. 20. Portion of a gill, seen from the ventral side. 



Fig. 21. Otocyst with its canal and nerve, and a portion of the cerebro-peda 

 commissure. A nerve frequently leaves the commissure near the otocystic nerve and 

 is distributed to the muscles of the foot. 



Fig. 22. Portion of the extremity of an otocystic canal, showing two closed 



pouches. 



