704 BEEP WATER MOLLUSES AND LRACHIOPOBS—DALL. vol.xvii. 



on this area are three large conical papillip, the largest and uppermost 

 standing in the median line. The outer mantle margin is thin and 

 smooth edged, covered in the natural state by a wide infold of the 

 epidermis. The secreting margin of the mantle is thickened with a 

 single row of conical short papilhe just within the edge; behind about 

 every fifth, and in front about every eighth papilla is distinctly largerthan 

 the average, and a little more set back from the edge. The pedal open- 

 ing is short and anterior. The foot, as in the L. papyracea, is relatively 

 large, glandiform, and byssiferous. The inner opening of the branchial 

 siphon is furnished with a circular smooth membranous valve. The 

 mouth is very large and funicular, the opening radiately striate; the 

 anterior palpi are indistinguishably merged with the membrane above 

 them, and their outlines can not be traced ; the posterior pair are adnate, 

 short, wide, and apron-like, not separated by a median sinus below. 

 From under them start the gills, which are attached by their outer 

 margins to an infolded nephridial lann'na, as in Halicardia; their inner 

 margins are bordered by a rather wide smooth membrane, with crenu- 

 lated edge, which appears to be attached in each case to that of the oppo- 

 site gill behind the foot, but the attachment is so delicate as to rupture 

 at the slightest strain, so that it leaves a doubt as to whether the junc- 

 tion all along the line is complete or not. Above the opposite border 

 is a narrow recurved free membrane corresponding to the ascending 

 limb of an ordinary gill, but which has no lamellte, and is i>erfectly 

 smooth. The main arterial stem of each gill extends to the siphonal 

 septum to which both are anchored, not, as in Halicardia^ being recurved 

 to join each other midway between the koel of the foot and the siphonal 

 septum. The inner edges of the gills at their commissure beliind the 

 foot are united firmly to the foot as in Halicardia. The heart is small, 

 with insignificant auricles, and the ventricle is pierced by the rectum, 

 which is large. The ovary, as in Halicardia, is enormous, of a yellowish 

 color, crannned with ova, which are discharged in a glairy mucus which 

 accumulates in the anal chamber. TJje structure of the gills recalls 

 that of Halicardia, but they are thicker, with fewer and more project- 

 ing lamelhf , more or less zigzag in their course. Aboye it is seen that 

 the longitudinal elements of the reticulum predominate over the trans- 

 verse branches, the contrary being the case in Halicardia. The infolded 

 lamina of the mantle in this species is longitudinally folded, and has a 

 free edge, and subcylindric posterior free end almost exactly as in Hali- 

 cardia. All parts of it are irregularly cavernous and filled with lobes 

 of the ovarian gland bearing ova in all stages, which appear to be dis- 

 charged into the anal chamber by a passage opening near the median 

 line on each side of the visceral mass behind close to the nei)hridial 

 orifice. 



In Pelseneer's account of the vai'ious species of Lyonsiella, described 

 in the Challenger report, no such free lamina of the mantle is described, 

 and the gills are represented distinctly, both in text and figures, as 



