ZOOLOGY: MARINE INVERTEBRATES. 91 



may be obtained on this shore, the encrusting species Membrani- 

 pora pilosa occurring on various seaweeds, while Crysia eburnea 

 and Cellepora ramulosa occur most commonly on the Chondrus , 

 Bugula turrita— often mistaken for a hydroid — is also a common 

 species attached to the rocks or seaweed. Membranipora pilosa 

 is recognized readily by the single layer of closely approximating 

 oblique cells which are arranged in alternating order ; and the rim 

 of each is furnished with one long hair and several spinous denticles. 

 Crysia eburnea is attached only basally and grows in the form of 

 little white bushy tufts, much branched and often forming a round 

 cluster. The cells are cylindrical in two rows, nearly opposite, 

 and bend outwards with a gentle curve, terminating in a circular 

 aperture. Cellepora ramulosa is a white calcareous dichotomously 

 branched species, with irregularly clustered cells, each with a mu- 

 cronate point on the margin of the aperture. It grows to a height 

 of two or three inches (Johnston). Alcyonidium hispidum, always 

 abundant on the open rocky shore, encrusts the stems of the Fu- 

 cus ; and with it occurs not infrequently the more delicate and 

 smaller species A. hirsutum. These two are perhaps our most 

 beautiful bryozoans when the polyps are fully expanded ; although, 

 when the polyps are contracted and the rough brown polypary 

 alone is seen at low tide, it is one of the least attractive objects. 



Spirorbis borealis, the common sedentary worm of this coast, 

 always may be found in the tide-pools, attached to Chondrus cris- 

 pus and other seaweeds. Many chaetopods, nemerteans, and pla- 

 narians occur also. The nudibranchs are represented by the 

 common and beautiful Dendronotus arborescens, which is abundant 

 in all the tide-pools. ^Eolis papillosa and ^E. rufibranchiata are 

 found likewise among the seaweeds in these pools. Their egg- 

 masses occur under small stones in the pools. Another gastro- 

 pod abundant in these pools is our northern limpet, Acmcea testu- 

 dinalis, which is found everywhere clinging to stones or shells. 

 Chiton (Trachidermon) ruber, although more common in the deep 

 water, from which it is brought up by the dredge, not infrequent- 

 ly occurs in these tide-pools. Clinging to rocks, and simulating 

 in color the rose-tinted encrusting corallines so common on the 

 stones and shells of these shores, it is distinguished with difficulty. 

 Around the margins of the tide-pools and on the seaweeds and 

 rocks exposed at low water, as well as crawling over the barnacle 

 beds, is the most abundant coiled gastropod of these exposed 



