193 



ON THE ANATOMY OF CERTAIN SPECIES OF SILIQUA AND ENSIS. 

 By H. H. Bloomek. 



Read Wth November, lOO-t. 



PLATE XII. 



I WISH, first of all, to express my indebtedness to Professor W. H. Dall, 

 of the United States National Museum, for liis kindness in permitting 

 me to examine tlie following specimens. 



1. SiLIQUA PATULA (Dixon). 



External Characters. 



The animal is straight along the dorsal surface, with the exception 

 of a slight ventral deflection about one-third of the distance from the 

 anterior end. The length from the anterior side of the anterior 

 adductor muscle to the posterior side of the proximal portion of the 

 siphon is 60 mm., and the depth at the anterior and posterior ends 

 27 mm. 



The mantle-lobes commence at the postero-dorsal surface of the 

 anterior adductor muscle, and, in passing anteriorly over it, are quite 

 separate from each other. Then they take a deep curve, and proceed 

 posteriorly about half-way along the ventral surface, when they 

 become concresced, so that the pedal aperture is a large opening 

 extending from the anterior adductor muscle to the point of 

 concrescence. Further, near the centre of the ventral surface, the 

 mantle-lobes have the appearance of being abruptly pressed in, and of 

 gradually resuming their normal condition as they pass anteriorly. 

 Around the whole of the edge of each mantle-lobe is a curious 

 foliated fringe. At the anterior end of the pedal aperture it is 

 inconspicuous, but, proceeding along the ventral surface, it increases 

 in size, and, near the centre, assumes a larger and more complicated 

 arrangement. At the posterior end it is again very small, and 

 becomes larger as it traverses anteriorly the dorsal surface. The 

 muscular flaps bordering the pedal aperture are weak. 



The siphon is deep and comparatively short. The proximal portion 

 is very muscular, while the anterior part of each lateral side 

 terminates in a powerful siphonal retractor muscle. The free portion 

 of the siphon is in one piece, the exhalent being separated from the 

 inhalent chamber by a very muscular wall. This divisional wall 

 extends to the anterior end of the proximal portion of the siphon. 

 The distal end of each siphonal chamber is bordered by a tentacular 

 fringe, with the tentacles more numerous at the dorsal and ventral 

 edges of the siphon, and the remaining portion of the siphon is 

 covered with a papillose integument. There is no fourth aperture. 



The gills are relatively short and deep. They lie well dorsally, and 

 reach as far as the wall dividing the siphonal chambers. The outer 



