Bb6 DEEP WATER MOLLUSKS AND BBACHWFODS—DALL. vol.xvii. 



It may be well to recall here the essential cliaracters of the anatomy 

 of the Verticordia acuticostata, the type of that genus. It has two 

 siphonal openings with their orifices fringed with several rows of 

 papillai; the anal siphon opens into a closed chamber, the tioor of 

 which is formed by a muscular fleshy septum imperforate except for the 

 passu ge of a short, stout, stopper like foot, around which the septum 

 fits closely; the lower surface of this septum is devoid of any append- 

 ages; on each side of the foot lies, adnate upon its surface, a small 

 elongate triangular gill resembling one of the oral palpi of ordinary 

 pelecypods, but separated by some distance from the oral aperture. 

 This gill is without doubt functional as a ctenidium, but may be homol- 

 ogous with the posterior palpus (a view suggested by the presence of 

 palpi in JSuciroa), a possibility which requires further investigation; at 

 all events no other organ (unless it be the general surface of the septum 

 and branchial chamber) is |)resent tor purposes of respiration. There 

 are no palpi about the mouth. The edges of the mantle are separated 

 only by a narrow opening sufficient to give passage to the foot. The 

 septum was homologized by me with the siphonal sex^tum of ordftifr^y 

 pelecypods, which was supposed to be extended forward to the visceral 

 mass as it is in Lophocardium, though in the latter genus the usual 

 functional gills are present. 



In Euciroa the following difi'erences may be noted: The opening 

 between the lobes of the mantle is ample, the foot laterally compressed, 

 though small, more nearly resembles the same organ in the average 

 pelecypod; both pairs of labial i)alps are present and free; while a sep- 

 tum exists, the posterior part of which is obviously formed by an exten- 

 sion forward of the siphonal septum, yet a large part of it is formed by 

 lamellar gills which extend backward from the visceral mass near the 

 mouth enclosing the foot, and have their edges connected with each 

 other on each side and with the tissue of the mantle laterally, so that, 

 as in Verticordia, a complete separation between the anal and the bran- 

 chial chamber is insured. These differences, which will be described in 

 full detail under the species about to be named, are quite sufficient to 

 justify the assignment of generic rank to the group separated by me 

 under the name of Euciroa. 



EUCIROA PACIFICA, new species. 

 Plate xxiii, figs. 2, 4; plate xxiv, tigs. 4, 5, 7, 8. 



Shell rounded, inflated, solid, brilliantly pearly within, of a frosty dull 

 white externally, covered with a very thin pale brownish epidermis^ 

 under which the shell is everywhere minutely granular and sculptured 

 with fine radiating lines of large, sometimes sharp-pointed and recurved, 

 granules, the rows being very close set posteriorly but with wider inter- 

 spaces toward the middle and anterior part of the valves; concentric 

 sculpture only of feeble incremental lines, visible chiefly near the basal 

 margin of the valves; beaks jDromiuent, full, much 'incurved, anteriorly 



