. Bulletin of the Natural History Museum Zoology. 56 ALLEN, SANDERS AND F. HANNAH. Fig. 85 Yoldiella subcircularis. Outlines of shells from the right side to show variation in shape. Specimens taken from Sta. BG VI DS 76, West European Basin. (Scale = mm). 50H 40 1 80- 70J 60 50- _ W\L H\L â _â â ⢠â â ⢠â â Sr PL\TL â¢I-,'* ⢠Length(mm) Fig. 86 Yoldiella subcircularis. Variation in ratios of height H/L, width W/L and postero-umbonal length PL/TL to length against length of subsamples from Sta. BG DS 76, West European Basin (closed circles) and Sta. Walvis QS 07, Cape Basin (c
. Bulletin of the Natural History Museum Zoology. 56 ALLEN, SANDERS AND F. HANNAH. Fig. 85 Yoldiella subcircularis. Outlines of shells from the right side to show variation in shape. Specimens taken from Sta. BG VI DS 76, West European Basin. (Scale = mm). 50H 40 1 80- 70J 60 50- _ W\L H\L â _â â ⢠â â ⢠â â Sr PL\TL â¢I-,'* ⢠Length(mm) Fig. 86 Yoldiella subcircularis. Variation in ratios of height H/L, width W/L and postero-umbonal length PL/TL to length against length of subsamples from Sta. BG DS 76, West European Basin (closed circles) and Sta. Walvis QS 07, Cape Basin (closed squares). America specimens. In contrast the small number of speci- mens from the Guyana Basin differ slightly in having a lower height/length ratio (significant at the level). Internal morphology (Figs. 87 & 88). In Y. subcircularis the volume of the mantle cavity is large compared with that of the body. A well-developed sense organ lies at the far anterior margin. The siphons are combined and the inhalent siphon is shorter than the exhalent and is open ventrally. Both siphons are thin-walled and a pair of lateral haemoco- eles are present in the junction between them. There is a moderately large siphonal tentacle, most frequently found on the left side. The feeding aperture is well-developed with areas of glandular mantle epithelium on each side which are probably extended in life as paired, broad flaps. For some distance anterior to these, the inner muscular lobe is particu- larly well-ciliated and it may be that the feeding area either is separated from the pedal gape by a ciliary junction or it is the region where pseudofaeces are formed. The adductor muscles are small, approximately equal in size, oblong in shape and lie close to the dorsal and anterior and posterior mantle margins respectively. The gill plates are relatively few in number (18 in a specimen mm). Tissue junctions join the demibranchs to the mantle dorsally. The gill plates
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Keywords: ., bhlconsortium, bookc, bookcentury1900, bookcollectionbiodiversity
