730 DEEP WATER MOLLUSKS AND BRACRIOPODS—DALL. yoL.xyn. 



Fig. 2. Euciroa pacifica, Dall, about twice natural size ; diagram showing a vertical 

 cross section of the animal behind the foot; o, 6, subumbonal parts of the -vis- 

 ceral mass, showing the superficial region occupied by the genital glands, 

 between which are seen the dorsal mantle margin and the proliferations which 

 enfold the teeth ; c, pericardial chamber, with h, the ventricle of theheart lying- 

 over on the right side and partly hiding v' , the right auricle, while v, the left 

 auricle, is fully exposed; below the ventricle is seen the rectum r, which here- 

 passes through the floor of the pericardium and is cut through in the nephridium 

 below; s, s, cross section of the thick connective tissue formed by an infolding 

 of the mantle below the pericardium, from the lower internal waJl of which 

 fine reticulated fibers radiate upward; this lamina would seem analogous to the 

 free nephridial lamina in Halicardia (fig. 3, s' n'), but is attached to the visceral 

 mass and shows a jelly-like solidity into which no ramifications of the ovary 

 extend; below this descend the stems of the gills (with two tubular blood pas- 

 sages), supporting the transverse gill-laminae, on the faces of which the radi- 

 ating lines represent, not plications, but radiating muscular fibers seen through 

 the transparent epithelium of the plates; the gill plates are represented as if 

 laterally extended, but in life they extend obliquely backward so that an exact 

 section would cut through a number of plates without showing their outline; 

 the darkly-shaded spaces above the gills are the anterior portions of the anal 

 chamber; /, the foot, above which is seen the circular section of the retractor 

 muscle; m, m', lobes of the mantle, showing columnar muscular fibers in section. 

 Drawn by W. H. Dall ; page 688. 



Fig. 3. Halicardia flexuosa, Vf.ehill, magnified about foxir diameters, diagram of the 

 vertical cross section of part of the body and gills, taken behind the foot looking 

 toward the siphons ; d' . dorsal junction of the mantle, below which \sr, the rectum 

 in section; d, subumbonal visceral niass; o v, the cavernous nephridium in which 

 are seen p, q, the branches of the retractor muscles, and c v, cavities in the general 

 mass of the partly glandular and partly fibrous tissue; c r, roof of a p, the pos- 

 terior part of th(ianal chamber ; s, downward continuation of the uejihridium ; s', 

 point where the free lamina is given off internally; <m, part of the downward 

 continuation of the mantle lobe of the left side, cut away below m; n, free ver- 

 miform posterior termination of the lamina; n' , free edge of the lamina, more 

 anteriorly; below and to the right of this is seen the junction of the lower 

 surface of the lamina and the outer margin of e the outer lamina of the left gill; 

 z, papilla on upper surface of the siphonal septum ; T), severed stem of the left 

 gill with bloodvessel in section, the stem recurves and joins h' , that of the right 

 gill near j, the point where both are soldered to the posterior keel of the foot; c, 

 inner lamina of the left gill, extending between j and h, and forming part of the 

 roof of the peripedal chamber. Drawn by W. H. Dall; page 6&7. 



Fig. 4. Euciroa pacifica, Dall, about three times natural size ; diagram of the animal 

 from below, with i, i, i', i', the mantle severed and turned back to expose the 

 parts ; a, position of the anterior adductor ; j), p', the palpi ; /, the foot surrounded 

 by the coalescent gills ; s, the siphonal septum ; x, cavity of the incurrent siphon ; 

 below which are outlined the areas occupied by columnar muscular tissue and by 

 dotted shading the glandular region of the mantle in front of the siphon. Drawn 

 by W. H. Dall; page 688. 



Fig. 5. Halicardia flexuosa, Yerrili.; diagramof theheart and rectum much enlarged, 

 for comparison with that oi Euciroa (fig. 2, /;, v, v')\ a, the rectum passing 

 through V, the ventricle, with, I, the left and, r, the larger right auricle. Drawn 

 by W. H. Dall ; page 697. 



Fig. 6. Halicardia flexuosa, Verkill, slightly enlarged; diagram of the soft parts 

 removed from the shell, side view; u, median papilla above h, the anal siphon ; 

 o-e, the extremities of the pedal opening between the mantle lobes; the ends of 

 the muscles are shaded. Drawn by W. H. Dall; page 697. 



