14 



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



be Y. lucida from the North West Atlantic and two closely 

 related north-east Atlantic species (Yoldiella iris and Yoldi- 

 ella inflata). 



We have examined material from the Zoological Museum, 

 Copenhagen, specimens identified by Verrill & Bush, the 

 Jeffreys collections in London and Washington and Scandinavian 

 material from a variety of sources which includes specimens 

 identified by Dr. Kurt Ockelmann in his study of Greenland 

 material. To prevent even more confusion we accept as our 

 baseline that specimens from Eastern Arctic and northern 

 temperate shallow water populations of the east Atlantic adja- 

 cent to the type locality and which are described in the earliest 

 accounts, as Yoldiella lucida s.s. We have also examined West 

 Atlantic material some of which was misidentified and which we 

 recognize as Y. lucida s.s. namely:- 



MCZ No. 137266 labelled Yoldiella inflata, S. Block 

 Island, 180- 190 m. 



MCZ No. 227737 labelled Yoldiella lucida V & B, off 

 Bradlees Bank, 120 m. 



MCZ No. 159722 (unlabelled). 



MCZ No. 202847 (which includes specimens from a num- 

 ber of Stations mixed together). 



MCZ No. 78292 labelled Sta. 2697, off Halifax N.S., 377 

 m. 



USNM No. 73172 labelled Y. lucida, 200 m. 



USNM No. 202847 labelled Gulf of Maine. Mixture from 

 several stations. 



Specimens misidentified as Y. iris in the U.S. National 

 Museum, but which are clearly Y. lucida s.s. :- 



USNM No. 74517 labelled Gulf of Maine, 172 m. 

 USNM No. 159717 labelled Gulf of Maine, 40m. 

 USNM No. 159718 labelled Gulf of Maine, 134 m. 



Samples of Y. lucida from the Skaggerak, loaned by the 

 University Museum, Copenhagen, agree well with the figure 

 of Sars (1878) and which Locard (1898) considered as the 

 type (Fig. 1). These are also very similar to the shallow water, 

 North American specimens referred to as Y. lucida and Y. iris 

 by Verrill & Bush (1898). These latter specimens are very 

 slightly more inflated but otherwise identical to the specimens 

 taken from North American Basin Stations 105 and 207 (Figs. 

 4&7). 



Thus, Y. lucida s.s. is found in Arctic and North Atlantic 

 waters at shelf and upper slope depths, including the northern 

 part of North America Basin, off Nova Scotia, Norwegian 

 Sea, Greenland, Iceland, Skagerak and West European 

 Basin. Depth range: 38-811 metres. 



Shell description (Figs. l-A & 15, Table 1). Shell elon- 

 gate, ovate, moderately inflated, inequilateral, irregular con- 

 centric ridges, partially opaque, umbos moderately large, 

 inwardly directed, proximal dorsal margin close to umbos 

 depressed in many but not all specimens, antero-dorsal and 

 postero-dorsal margins raised to form sharp, low, keel on 

 either side of umbo, distally antero-dorsal margin extends in 

 almost straight line to point opposite anterior limit of hinge 

 plate then curves to the anterior margin, ventral margin long, 

 even curve, distal postero-dorsal margin slopes in almost 

 straight line, close to dorsal limit of posterior margin maybe 

 slightly upturned, limit of posterior margin supramedial, 

 slightly truncate, postero-ventral margin not sinuous, but 

 may be slightly flattened; hinge plate moderately broad, 



Fig. 2 Yoldiella lucida. Lateral views of shells from off the 

 northeast coast of America; a, USNM No. 73172, 200 m; b, 

 USNM No. 74517 labelled Yoldiella iris. Gulf of Maine, 172 m; 

 USNM No. 159717 labelled Yoldiella iris, 40 m. (Scale = 1.0 

 mm). 



c, 



except where narrow below umbo, anterior plate elongate 

 extends opposite anterior margin of adductor muscle, poste- 

 rior plate relatively short, does not reach posterior margin of 

 posterior adductor muscle, hinge teeth chevron-shaped, mod- 

 erately stout, maximum of 14 recorded in each series, occa- 

 sionally anterior series has one more tooth than posterior; 

 ligament amphidetic, moderately elongate, anterior and pos- 

 terior lobes extend ventral to hinge plate. 

 The above description is of a fully grown animal. In smaller 



Fig. 3 Yoldiella lucida. Outline drawings of shells from the right 

 side from Sta. 105 to show change in shape with increase in size. 

 (Scale = 1.0 mm). 



