ON LARVAE OF LINGULA AND PELAGODISCUS (DISCINISCA). 



67 



Simroth, H., " Die Brachiopoden der Plankton-Exped.," Ergebn. Plankton-Exped., Bd. ii, F.f., 19 pp. 



1 Taf., 1897. 

 Yatsu, N., "On the Development of Lingula anatina," Jour n. Coll. Sci. Imp. Univ. Tokyo, vol. xvii, 



art. 4, 112 pp., 8 pis., 1902. 

 Yatsu, N., "Notes on Histology of Lingula anatina," op. cit., art. 5, 29 pp. 2 pis., 1902«. 

 Yatsu, N, "Notes on the young Discinisca," Zool. Anz., Bd. xxix, pp. 561-5G3, 19(Jo. 



DESCRIPTION OF THE PLATES. 



List of Reference Letters. 



A. Anus. 



A.S. Arm-sinus. 



B.M. Brachial muscle. 



B.M.T. Transverse brachial muscle. 



B.W. Wall of body proper. 



C. Cirrus. 



CI, C4, Cll, CI 3. First, fourth, eleventh, 



thirteenth cirrus. 

 CD. Coelomoduct. 

 Ch. Cha?ta. 

 Ch. I, Ch. II, Ch. Ill, Ch. IV, Ch. V. First 



to fifth large chsetre of Pelagodiscus. 

 Ch. S. Slender clnetse. 

 Co. Coelom. 



Co. E. Ccelomic epithelium. 

 D.B. Dorsal blood-vessel. 

 D.M. Dorsal mesentery. 

 E. Epistome. 



G.C. Gland-cells in mantle. 

 G.L. Lateral nerve-ganglion. 

 G.P. Gastro-parietal band. 

 G.V. Ventral nerve-ganglion. 

 H.L. Hinge line. 

 In. Intestine. 



L.A.D. Anterior dorsal lobe of "liver." 

 L.M. Lateralis muscle. 

 L.P.D. Posterior dorsal lob of "liver." 

 L.V. Ventral lobe of " liver." 

 M. Mantle. 



M.G. Mid-gut. 



M.M. Mantle-margin. 



M.M.D. Margin of dorsal mantle. 



M.M.V. Margin of ventral mantle. 



Mo. .Mouth. 



M.T. Thickened area of mantle. 



N.T. Nervous tract. 



CE. CEsophagus. 



O.A. Anterior occlusor muscle. 



O.I. Obliquus internus muscle. 



O.P. Posterior occlusor muscle. 



P. Pigment. 



P.D. Dorsal protegulum. 



Pe. Peduncle. 



Pe. E. Epithelium of peduncle. 



Pe. M. Muscles of peduncle. 



Pr. Periostracum. 



P.S. Pigment-spot ("eye"). 



P.V. Ventral protegulum. 



S. Shell. 



Sc. Statocyst. 



S.M. Shell-margin. 



S.M.D. Margin of dorsal shell-valve. 



S.M.V. Margin of ventral shell-valve. 



S.S. Supporting substance. 



St. Stomach. 



T. Tentacle. 



T.M. Transverse muscles. 



Plate IV. 



Lingula anatina Bruguiere. 



Figs. 1, 2. Outlines of ventral (fig. 1) and dorsal (fig. 2) shell-valves of youngest larva obtained 

 ("52 mm. long). The protegulum, or primary shell, is seen in each valve. See p. 48. ( X 39.) 



Fig. 3. Outline of ventral shell-Valve of a larva PI mm. long (larva c, group iii, p. 49). ( X 39.) 



