42 



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





QS01 2634 



322 



50°14.4'N 



13°10.9'W 



OS 



30. 



7.76 











50<T5.2'N 



13°11.0'W 











WS01 2550 



221 



50°19.4'N 



13°08.1'W 



ws 



30. 



7.76 











50°19.3'N 



13°06.9'W 











WS02 24S 



287 



50°19.3'N 



12°55.8'W 



ws 



30. 



7.76 











50°20.0'N 



12°56.0'W 











CP10 4823 



2 



48°25.5'N 



15°10.7'W 



CP 



31. 



7.76 











48°26.3'N 



15°09.8'W 











WS03 4829 



1 



48°19.2'N 



15°23.3'W 



ws 



1. 



8.76 





(broken valve) 



48°19.1'N 



15°22.5'W 











WS07 4281 



5 



47°30.6'N 



9°37.1'W 



ws 



7. 



8.76 











47°31.2'N 



9°35.7'W 











DS14 4254- 



1 



47°32.6'N 



9°35.7'W 



DS 



7. 



8.76 







4307 





47°32.9'N 



9°35.1'W 











OS06 4316- 



2 



46°27.3'N 



9°36.2'W 



OS 



9. 



8.76 







4307 





47°27.9'N 



9°36.0'W 











DS16 4268 



7 



47°29.8'N 



9°33.4'W 



DS 



9. 



8.76 











47°30.3'N 













QS07 4249 



2 



47°36.8'N 



9°34.3'W 



OS 



10. 



8.76 











47°31.3'N 



9°34.3'W 











QS08 4327 



1 



47°29.8'N 



9°39.2'W 



QS 



11. 



8.76 











47°29.5'N 



9°38.8'W 









NORTH AMERICA BASIN 













Atlantis II 



62 



2496 



25 



39°26.0'N 



70°33.0'W 



ET 



21. 



8.64 



12 



64 



2886 



80 



38°46.0'N 



70°06.0'W 



ET 



21. 



8.64 





72 



2864 



120 



38°16.0'N 



71°47.0'W 



ET 



24. 



8.64 





73 



1330- 

 1470 



1 



39°46.5'N 



70°43.3'W 



ET 



25. 



8.64 



Chain 50 



76 



2862 



53 



39°38.3'N 



67°57.8'W 



ET 



29. 



6.65 





78 



3828 



3 



38°00.8'N 



69°18.7'W 



ET 



30. 



6.65 





85 



3834 



32 



37°59.2'N 



69°26.2'W 



ET 



5. 



7.65 





87 



1102 



17 



39°48.7'N 



70°40.8'W 



ET 



6. 



7.65 



Atlantis II 



126 



3806 



14 



39°37.0'N 



66°47.0'W 



ET 



24. 



8.66 



24 









39°37.5'N 



66°44.0'W 









Chain 106 



334 



4400 



5 



40°42.6'N 

 40°44.0'N 



46°13.8'W 

 46°14.6'W 



ES 



30. 



8.72 





335 



3882- 

 3919 



12 



40°25.3'N 



46°30.0'W 



ES 



31. 



8.72 



Knorr 35 



340 



3264- 



95 



38°14.4'N 



70°20.3'W 



ES 



24.22.73 







3356 





38°17.6'N 



70°22.8'W 









We have examined the Verrill & Bush material housed in 

 the U.S. National Museum. With the exception of specimen 

 No. 49390, which is more inflated and slightly more inequilat- 

 eral than is typical of specimens of Y. inconspicua and which 

 is probably Y. frigida, the Verrill & Bush collection is 

 correctly described. 



Waren (1989) synonymizes Y. inconspicua with Y. nana. 

 We disagree with this view. Y. nana is essentially a high 

 latitude species from the shelf and upper slope while Y. 

 inconspicua s.s. is restricted to temperate latitudes at lower 

 slope to abyssal depths in the North American and West 

 European Basins. 



Depth range: 1102^829 m, but most common between 

 2400-3000 m. 



Shell description (Fig. 61). The shell is very well 

 described by Verrill & Bush (1898). We would add that 

 although the shell is small, compressed and an ovate wedge- 

 shape, the width, height and thickness of shell for any given 

 length is variable (Fig. 62). Some specimens have a slightly 

 sinuous postero-ventral margin. In many specimens the gut 

 and internal organs are visible through a transparent shell, in 

 others light and dark banding patterns are present on thicker 

 shells. Hydroids may be present over most of the shell 

 margin. The large elongate, slightly 'saddle-shaped', internal 

 ligament is characteristic. The hinge teeth are small, the total 

 number ranges from 6 in an individual 2.42 mm in length to 

 13 in an individual of 3.44 mm in length. There is normally an 



Fig. 61 Yoldiella inconspicua inconspicua. Lateral views of shells 

 from the right side and detail of hinge from a right valve; a, 

 variation in shape of three specimens from Sta. 76 North America 

 Basin with b, a specimen from Sta. INCAL CP 06 West European 

 Basin. (Scale = 1.0 mm). 



additional tooth in the anterior series (3/3-7/6). Although the 

 shape varies between individuals there is an overall trend of a 

 slight increase in posterior umbonal length and in width with 

 increasing shell length. The height ratio remains more or less 

 constant (Fig. 62). Analysis of shell length of two samples 

 from the east and west Atlantic showed marked size differ- 

 ences (Fig. 64) probably indicative of the differences in time 

 of successful settlements. Individual peaks in the sample from 

 the Bay of Biscay perhaps might indicate an annual breeding 

 event and a lifespan of 5 or 6 years. 

 Shell measurements (mm) & ratios are as follows:- 



Length 



Height 



Width 



H/L 



W/L 



PL/TL 



4.20 



2.87 



1.66 



0.68 



0.39 



0.53 



4.03 



2.78 



1.54 



0.69 



0.38 



0.51 



3.79 



2.71 



1.53 



0.71 



0.40 



0.50 



3.66 



2.45 



1.43 



0.66 



0.39 



0.53 



3.58 



2.50 



1.38 



0.70 



0.38 



0.50 



3.41 



2.75 



- 



0.72 





0.53 



1.49 



1.02 



0.54 



0.69 



0.36 



0.48 



0.99 



0.76 



- 



0.77 



- 



0.48 



0.93 



0.62 



- 



0.67 



- 



0.50 



Internal morphology (Fig. 63). The morphology of the 

 mantle is essentially the same as in other nuculanoid species. 

 There are typically three mantle lobes. Specialization of the 

 mantle margin includes an anterior sense organ, in position 



