154 MEMOIRS OF THE UNIVERSITY OP CALIFORNIA 



Amphidinium truncatum sp. nov. 



Text figure U, 3 



DiAGXosis. — A small species witli sar-klike body, its length 1.2 transdianieter. 

 dorsoveutrally compressed to 0.5 trausdiameter ; epicoue low, squarely truncate, 

 left antapex pointed; sulcus confined to striate hy|3ocone; pale green; littoral 

 habitat. Length, 38m. Pacific at Tja Jolla, California, Jidy, August. 



Description. — The body is stout, its length 1.2 trausdiameter, dorsoventrally compressed to 

 0.5 trausdiameter. The epicoue is 0.2 of the total length in height, and squarely truncate. Its 

 form above the girdle is that of a very low, truncate, ellipsoidal cone, whose major and minor 

 axes in its base are respectively 0.67 and 0.33 trausdiameter and truncate apex 0.50 and 0.25 

 respectively. Its short side has a slope of about 40°. There is a noticeable suppression of the 

 asj'mraetry of the epicoue so characteristic of ^i. asi/mmctricum and A. operculatum. The 

 hypocone is rotund, its length 0.8 of the total length and about equal to its greatest trausdiameter 

 which is located near the middle. Its left side is less convex than the right and it shares M'ith 

 the epicone the considerable doi'soventral compression. Anteriorly it spreads abruptly below 

 the girdle in a squarish shoulder, thereby increasing the width (transversely) at that level 25 

 per cent more than that of the epicoue. The antapex is broadly rounded with a low symmetrical 

 rounded part on the right side of the deeply excavated posteriorly flaring sulcus, and a sharp 

 point on the left which projects less than a furrow's width beyond the general contour. 



The girdle is sjTumetrical, located 0.12 of the length below the apex. Its course is nearly 

 horizontal except at its proximal and distal ends which form an almost symmetrical V-shaped 

 junction on the ventral face about as long as the epicone. The furrow is broad. 0.12 trans- 

 diameter, aud .shallow. The sulcus is confined in the hypocone, is about two-thirds the width of 

 the girdle, has a verj- slight sigmoid curvature and widens posteriorly to 0.2 trausdiameter. It 

 is deeply excavated to the middle of the body posteriorly at a point just below the junction of 

 the ends of the girdle. It has no flap on its left side, but is open throughout its course. Both 

 margins are continued beyond the antapex in a short projecting, more or less pointed tooth, the 

 left being the longer. The longitudinal flagellum arises from a pore at the proximal end of the 

 sulcus, just behind the anterior flagellar pore. It extends posteriorly beyond the body for 0.83 

 of the total length. 



The surface is uniformly striated on the hypocone with equidistant, parallel faint lines, about 

 twenty across the dorsal face. No lines can be detected on the short slopes of the epicone. The 

 peripheral pellicle surrounding the body is very distinct. The nucleus is an ellipsoidal, sub- 

 reniform body located in the left posterior part of the hypocone with its long axes pa.ssing from 

 the left anteriorly, to the right posteriorly. It is a little more than 0.5 of the trausdiameter in 

 length, its minor axis is a trifle more than 0.5 of the major, and it shares in the general dorso- 

 ventral compression. A large pusule opens into the anterior flagellar pore and is connected b}' 

 a narrow canal with a smaller, circular pusule farther posterior and on the right side of the 

 body. A halo of subspheroidal, bluish green chromatophores fills the peripheral layer of 

 ej'toplasm. The general color is a diffuse pale pea green. 



DiMENSioxs. — Total length, 38/^; greatest transdianieter, 30^; dorsoventral 

 diameter, 15m. 



OccuEREXCE. — ^^^ery abundant in the beach sand off La Jolla, California, 

 during July, 1914. It lives in laboratory aquaria for two to three days, but 

 becomes inactive very quickly when exposed to the illumination of the 

 microscope. 



