ZOOLOGY : MARINB INVERTEBRATES. 



81 



vorable to its existence, although it seems to be the natural habi- 

 tat of a number of closely related species. On the stems of Lam- 

 inaria, various bryozoans as well as Spirorbis commonly are found ; 

 and Parypha crocea sometimes covers them thickly. Among the 

 roots, besides many deep-water shells, the more delicate species 

 of hydroids are not uncommon. Clytia poterium and C. bicophora 

 are frequent. Their usual habitat is in rocky tide-pools where the 

 water is clear and cool. They are attached almost invariably to 

 seaweeds, or the stems of other hydroids ; and, according to Agassiz, 

 never to solid rock or to immovable substances. C. poterium has 

 the summits of its campanulate oalices smooth, and the gonophores 



I'arypha eroeea. Corymorpha pemUda. Clava leptostyki^ 



(After Feirkes, by courtesy of the Eesex Institute.) 



arise from the creeping stolon. The pedicels of the nutritive zo- 

 oids are strongly ringed from top to base. C. bicophora is distin- 

 guished from the last by the notched margins of the calices, the 

 anaulated gonophores which arise from the stolons or the stems, 

 and the weakly ringed condition of the pedicels of the nutritive 

 zooids. 



On the ledges near the mouth of the estuary several species 

 of hydroids and other littoral animals always may be obtained. 

 Among the former is Clava leptostyla, which can be found here in 

 abundance at any season of the year. It is attached to Fucus 

 and Ascophyllum, and more rarely to the rocky bottoms of the 

 pools. In the former case it is exposed at low tide, commonly 

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