. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Figure 1. Prisfigloma nifens (Jeffreys). Internal view of the right valve of a specimen from the original type collection (Specimen 197414, National Museum, Jeffreys Collection, PORCUPINE Expedition, Station 31, 1381 fathoms). permanently in the midline but hang down- wards as very short fingerlike processes. The ctenidial axis is not muscular. It ex- tends posteriorly beyond the first pair of gill plates as a free, tapering projection. Thus the hypobranchial cavity is not en- tirely separated off from the remain
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Figure 1. Prisfigloma nifens (Jeffreys). Internal view of the right valve of a specimen from the original type collection (Specimen 197414, National Museum, Jeffreys Collection, PORCUPINE Expedition, Station 31, 1381 fathoms). permanently in the midline but hang down- wards as very short fingerlike processes. The ctenidial axis is not muscular. It ex- tends posteriorly beyond the first pair of gill plates as a free, tapering projection. Thus the hypobranchial cavity is not en- tirely separated off from the remainder of the mantle cavity. The paired palps are large and broad and extend from either side of the mouth to the posterior edge of foot; the palp proboscis originates at the pos- terior dorsal junction of each palp. The contraction of palps and palp proboscides in preserved specimens makes their use in taxonomy questionable. The inner faces of the palps have a large number of folds (22-25) with a morphology essentially sim- ilar to that described by Stasek (1961) for Acila. The foot is broad with a divided sole; it is moderately large with numerous papillae along the margins. The sole of the foot is ciliated, densely so along cen- tral groove and just lateral to it, while the remainder of the sole is sparsely ciliated. A so-called "byssal" gland is present. It is moderately large, ovoid in structm-e with a central cavity enclosed by glandular secret- ing cells, and partitioned in a Figure 2. Prisfigloma nitens (Jeffreys). Internal view of left and right valves of specimens from the Gay Head- Bermuda transect, with enlargements to show detail of hinge structure. sagittal plane. Each half opens, side by side, venti-al to the heel of foot just poste- rior to the limit of the di\'ided sole. The mouth lies close to, but not abutting, the anterior adductor muscle. The oesopha- gus passes anteriorly and dorsal to adduc- tor before turning posteriorly to join a r
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