18 J.A. ALLEN, H.L. SANDERS AND F. HANNAH 



Table 1 Yoldiella lucida; numbers of anterior and posterior hinge teeth in specimens from different localities. 





Biscay 







North Atlantic 







'Thor' N. 



European 







Length 



Teeth 



No. 



USNM. 



Length 



Teeth 



No. 



Length 



Teeth 



No. 





(mm) 



Ant. 



Post. 



No. 



(mm) 



Ant. 



Post 



(mm) 



Ant. 



Post. 



INCAL DS 02 



2.28 



6 



6 



738419 



3.07 



8 



8 



2.50 



8 



7 



INCAL DS 01 



2.42 



7 



7 



159718 



3.22 



10 



10 



2.77 



8 



9 



INCAL DS 01 



2.75 



7 



7 



74517 



3.35 



11 



10 



2.91 



9 



9 



INCAL DS 01 



2.95 



8 



8 



202847 



3.84 



11 



11 



3.44 



9 



9 



INCAL CP 01 



3.24 



9 



9 



202847 



3.94 



11 



11 



3.49 



9 



10 



INCAL DS 01 



3.28 



8 



8 



202847 



4.03 



11 



10 



4.31 



11 



11 



INCAL CP 01 



3.49 



8 



8 



202847 



4.51 



12 



12 



4.39 



12 



12 



INCAL DS 02 



3.57 



9 



9 



202847 



4.67 



11 



11 



4.67 



11 



11 



POLYGAS 























DS26 



3.61 



11 



11 



73172 



4.93 



12 



12 



5.02 



11 



12 



INCAL DS 01 



3.77 



10 



10 



202847 



5.98 



12 



14 



5.02 



14 



14 



INCAL DS 01 



4.31 



10 



10 



202847 



6.02 



15 



14 



5.10 

 5.10 

 5.10 

 5.10 

 5.19 

 5.61 



13 

 11 

 11 

 13 

 12 

 13 



14 

 12 

 12 

 13 

 11 

 13 



Very similar to Y. lucida (for points of difference see 

 p. 19), past records e.g. (Verrill & Bush, 1898; Waren, 1989) 

 testify to this. 



Internal morphology (Fig. 10). The internal morphology 

 is similar to that of Y. lucida. There is a well-developed 

 ciliated anterior mantle sense organ. The inhalent and exhal- 

 ent siphons are combined for most of their length, and the 

 inhalent siphon is not fused along its ventral margin. The 

 siphonal tentacle is well-developed and usually attached to 

 the left of the base of the siphons. The feeding aperture is 



Fig. 9 Yoldiella obesa obesa. Lateral views of shells from the right 

 side to show change in shape with increasing size and detail of 

 hinge plate. Specimens from Sta. 62 North America Basin. Note 

 adductor muscles and hind gut loop seen through the transparent 

 shell. (Scale = 1.0 mm). 



also well-developed and provided with numerous gland cells. 

 The broad and, in preserved specimens, convoluted part of 

 the inner muscular lobe which forms the feeding aperture, 

 extends anteriorly beyond the limit of the aperture and is 



Fig. 10 Yoldiella obesa obesa. Lateral views of the internal 

 morphology from right and left side. (Scale = 1.0 mm). 



