THE COAST OF CALIFORNIA. 103 



ops into a planula in its sac, and separating from this 

 . organ follows a similar course of development in one or 

 two other genera of hydroids. If this supposition be cor- 

 rect, this is an exceptional method of development for this 

 genus. 



POLYORCHIS PENICILLATA A. Ag. 



(PLATE IV, FIGS. 6, 7.) 



Many specimens of this Medusa were found near the 

 wharves at Santa Barbara, Santa Cruz and San Francisco. 

 The jelly-fish is very conspicuous on account of the circles 

 of dark-purple tentacular bases and the extended wreath 

 of the tentacles. It is the most magnificent of all the west 

 coast Hydromedusae which were observed. 



The bell is large, about one and one-half times as high 

 as broad. It has a slightly yellow color and a small, 

 rounded apical prominence. The bell walls are thin and 

 of about uniform thickness throughout. 



Radial tubes four. Each radial tube has lateral branches 

 which arise in pairs opposite each other. These lateral 

 branches often subdivide or become forked at their ends. 

 The largest subdivisions are situated about half the dis- 

 tance from the apex of the bell to its margin. The lower 

 extremities of the four radial tubes, at their junction with 

 the circular tubes, are ordinarily destitute of lateral ap- 

 pendages. The motion of the bell is sluggish, not unlike 

 that of Nemopsis. 



The length of the tentacles is greater than the altitude 

 of the bell, and these organs are ordinarily, when at rest, 

 carried at right angles to the bell walls. A. Agassiz found, 

 in the specimen which he described, thirty-six tentacles, 

 or eight between each pair of tentacles which hang from the 

 neighborhood of the junction of the radial and marginal 

 canals. In the largest specimens which were taken at 



