270 PROCEEDINGS OF THE ACADEMY OF [1889. 



species is a remnant of the original ligament or a mere epidermal 

 extension. 



The length of the contracted specimen examined was 270"0 mm. 

 It was obtained on the Florida coast. 



Very different in some particulars is the macroscopic anatomy of 

 ZirpJuea crispata of which a specimen, measuring in its contracted 

 state 260.0 mm., is before me. It was obtained by Dr. R. E. C. 

 Stearns, in Puget Sound, Washington Territory. In this species the 

 si phonal tube is covered with a dehiscent thin papery epidermis, as 

 in Mya. and is about three times as long as the rest of the animal, 

 proportionally thicker, more cylindrical and consequently more 

 bluntly pointed than in P. costata. There are no important differ- 

 ences in the pedal opening where the curtain is close to, if not 

 coalescent with, the margin of the mantle. The ventral portion of 

 the visceral mass is not flattened and marginated, as in P. costatus, 

 but is produced into a point behind. Above this point there is no 

 sensory appendicle. The palpi are much as in P. costatus and 

 similarly supported by the umbonal apophysis on each side, but the 

 lower or inner palpus is much less fleshy. The gills join behind the 

 body but the junction is not floored across and hence there is no- 

 separation of the anal and branchial chambers, nor does the siphonal 

 septum make its appearance where the siphon begins. On the con- 

 trary the siphon incloses but a single tube and only at about the 

 distal third of its length does any division or partition appear. All 

 this distance the somewhat attenuated gills extend, nearly filling the 

 tube, and united at their bases. The gills on each side consist of a 

 W-shaped pair of sacs, but the outer stem of the W is not produced 

 into an appendicular lamella as in P. costatus. The anus is thin- 

 edged with a valvular infolding of the edge but less cup-shaped than 

 in P. costatus. Following the line which would have been taken by 

 the siphonal septum, had it existed, are two double-edged, little- 

 elevated ridges. It is probable that the stem of the gills so ex- 

 panded in life as to conduct the effete products of the intestine to 

 the anal tube of the siphon without allowing them to come in con- 

 tact with the respiratory face of the gills. Taken as a whole 

 Zirphaxi seems more modified than Pholas and shows fewer traces 

 of the Myacean type from which both are probably descended. 



I have not found a description of the soft parts of these two 

 species, after some search in the text books, and so have thought it 

 well to put them on record. 



