. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Deep-Sea Protobranchs • Allen and Sanders 283 Gills well developed with 27-35 plates to each side of the axis, and extend along the body to a position opposite the posterior limit of the stomach; no muscles in the sus- pensory part of the axis and in sectioned specimens the axial blood space is excep- tionally large (Fig. 22). Palps, bearing about 35 ridges, centrally located in the mantle cavity and lie relatively close to the ventral edge of the shell. Body and foot large, the dorsoventral axis turned through 90°. &
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Deep-Sea Protobranchs • Allen and Sanders 283 Gills well developed with 27-35 plates to each side of the axis, and extend along the body to a position opposite the posterior limit of the stomach; no muscles in the sus- pensory part of the axis and in sectioned specimens the axial blood space is excep- tionally large (Fig. 22). Palps, bearing about 35 ridges, centrally located in the mantle cavity and lie relatively close to the ventral edge of the shell. Body and foot large, the dorsoventral axis turned through 90°. "Byssal" gland moderately large and the fringing papillae of the foot variable but relatively small in size. Mouth set far back from the anterior ad- ductor muscle; the oesophagus extends di- agonally anteriorly and dorsally towards the anterior adductor; however, unlike S. frag- ilis, it turns short of the posterior edge of the muscle towards the stomach. Stomach large, but proportionately smaller than in other species of SiUcuIa. Combined style sac and midgut large and elongate, the long axis oriented in a more dorsoventral direc- tion than in the previous two species. Hind- gut curving downwards anteriorly towards the pedal ganglion before passing dorsally to the right side of the body where it forms a single, small loop. There is no U-bend in the hindgut behind the style sac. Both cere- bral and visceral ganglia small, elongate and cylindrical in shape. Kidney more ex- tensive than in S. filatovae and S. fragilis, invading the body behind the stomach (Fig. 21). Remarks. SiUcida mcalesteri is possibly conspecific with Silicula patagonica (Dall). We have examined the type specimen of S. patagonica ( Nat. Mus. No. 96914; Fig. 23) and the single valve lacks the umbonal region together with the proximal parts of the anterior and posterior hinge plates. In addition, the posterior shell mar- gin is badly eroded, and the anterior shell visceral ganglion posterior pe
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