85 



NOTE ON THE ANATOMY OF RESANIA, Ghay, AND ZENATIA, Gray. 



By Dr. W. H. Dall, 



Hon. Curator, Department of Mollusks, U.S. National Museum, 



"Washington. 



Eead loth April, 1898. 



I HAVE recently been able to examine alcoholic specimens of Resania 

 lanceolata (otherwise known as Vanganella Taylori), Gray, and Zenatia 

 Deshayesii, Reeve, from New Zealand. These were collected where 

 they had been thrown up by the waves, and were so permeated with 

 fine siliceous sand that thin sections could not be cut for fear of 

 ruining the microtome. They were, however, otherwise perfect, 

 and, since the anatomy of these forms has not been described, it 

 seems desirable to give some account of the more conspicuous features 

 of their structure. 



Eesania lanceolata, Gray. 



In this very inequilateral form the j)osterior part of the valves is 

 disproportionately short, and the pallial sinus is short, extending 

 forward only to the thickened ray which passes downward from the 

 umbonal region of the valve. The siphons are naked, slender, closely 

 united to their very tips, the orifices nearly in the same plane and 

 surrounded by small papillae, much retracted in the specimens. 



The mantle has a thickened edge, smooth for the most part, but, 

 near the ends of the shell, more or less papillose, with rather distant 

 papillae. The mantle is completely open, except in the central portion 

 of the dorsal margin, not being united even Avhere its margins pass 

 around the adductors. The foot is compressed, sharp-edged, pointed, 

 large and muscular, with no obvious byssal groove, and of a lanceolate 

 outline. Its edges are entire. The palpi are large, narrow, long, 

 smooth externally, plicate internally, adherent near the small circular 

 mouth. They extend beyond the posterior edge of the visceral mass, 

 becoming distally free and twisted at the ends. The body is connected 

 with the siphonal septum by a Q- shaped fleshy septum, from which, 

 on each side, a smooth, fleshy, narrow flap, as long as the septum itself, 

 hangs down into the branchial chamber. Outside these flaps, and 

 seated on the lateral borders of the fleshy septum, are the gills. These 

 present some peculiar features, the most obvious of which is that the 

 gills of the two sides are not symmetrical ; and, further, that on one 

 side, and in some cases on both sides, the plicate laminae are dis- 

 continuous. 



The ctenidium of the left side is short and small, the outer lamina 

 smaller than the inner, both dwindle to a point and cease before 

 reaching the vertical of the visceral mass, and there is a distinct 

 vacant space with no trace of a pendant lamina between the anterior 

 termination of this part of the ctenidium and the sinus between the 

 posterior parts of the palpi. Further forward, between the upper and 

 lower palpi, a new lamina, corresponding to the inner direct and 

 reflected lamina of the ctenidium, is developed and attains a respectable 

 size, being wider than the palps and extended forward, diminishing in, 



