NATURAL SCIENCES OP PHILADELPHIA. 161 



from the Bay of Fundy. We have a third species from Behring's Straits, and 

 that described below makes a fourth. 



Chelysoma producta. 



All other known species of this genus are remarkable among Ascidians for 

 their depressed form, the body being very short, sessile, attached by their 

 flattened anterior extremity, to which the broad disk is parallel, and forms 

 nearly the whole of the part of the body which is exposed to view. In C. 

 producta, on the contrary, the anterior part of the body is much produced, 

 laterally compressed, and longer than the disk is broad, while its attachment 

 is inferior and usually very narrow. In well-formed specimens the dorsum 

 is compressed and arched with a well-marked carina, beneath and parallel 

 with which the rectum may be seen through the translucent test. The disk 

 is obliquely placed, and its margin projects strongly beyond the sides of the 

 body. Its surface is divided into 14 polygons, 4 — 5 sided, beside the two 

 which contain the apertures, each of which latter is again subdivided into six 

 triangular valves. 



In our largest specimens the body is 1-5 inch in length, and 0-5 broad at 

 the middle ; the disk is 1'08 high and 0-81 broad. 



It is usually attached to Sertularians. 



Dredged by Lieut. White in " 8 to 12 fathoms, shelly, off the N. W. point of 

 Lummi Island." 



HOLOTHURIADAE. 



Pbntacta pipehata. 



Allied to P. frondosa. Body ovate, smooth and glabrous, of a yellowish 

 color, speckled and spotted with black. Sucking feet retracted in our speci- 

 mens, not numerous, and arranged in five irregular rows. Tentacula short 

 and broad, ramose. Length (contracted) lj inches : breadth, 0'8 inch. 



We find three or four specimens in the collection, none of them with pro- 

 truded tentacles. 



Pentacta populifer. 



Body thick-fusiform in shape. Surface entirely covered with minute, per- 

 forated, polygonal, calcareous plates, each plate having from twenty-five to 

 forty holes, and being armed with a sharp umbo or spine at the centre of its 

 outer surface. Sucking-feet small, of moderate length, very numerous, and 

 arranged in five regular double rows, extending from one extremity of the 

 body to the other. Tentacula ten, eight large and two small ; the large ones 

 of elongated form, and shaped like Lombardy poplar trees, (Populus dilatata), 

 branching nearly from the base ; branches short. The small tentacles are 

 placed together, and are minute, not a tenth part as long as the others. 

 Length of the largest specimen 2 inches ; usual length from 1 to 1J inches. 



From the number of specimens collected we judge this species to be com- 

 mon in the Sound. It is found in the circumlittoral zone. 



The Influence of the Earth's Atmosphere on the Color of the STA3JS. 



BY JACOB ENNIS. 



From the small amount of attention paid to the colors of the stars as a dis- 

 tinct branch of physical research, a vague and indefinite impression has been 

 somewhat prevalent that the atmosphere of our earth has great power in 

 producing the apparent colors and the changes of colors of the fixed stars. 

 The subject is highly important. During the last two or three years it has 

 occupied much of my attention, and I propose in this paper to present my 



1864.] 11 



