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GUIDE TO LOCALITIES. 



are lined with the drooping rockweed, and in their depths may 

 be seen a luxuriant growth of the more delicate algae, especially 

 Ulva and C/iondrus crispus, the latter reflecting beautiful blue 

 and purplish colors from their oily surfaces wherever the sunlight 

 strikes thera. Coralline seaweeds are also very common, and among 

 them the deep and clear-water mussel Modiola modiolus. Its sur- 

 face commonly is covered with the pinkish encrusting Corallina, and 



Hvbocodon. 



Coriine mirahtUs. 

 (After Fen-kes, by courtesy of the Essex Institute.) 



rough with projecting epidermal spines ; features which serve ad- 

 mirably to disguise the presence of the mollusc. Attached to these 

 mussels we find not infrequently the more delicate species of hy- 

 droids, which are unable to withstand the exposure to which the 

 more hardy littoral species are subjected. Among tubularians, 

 Endendrium, dispar and Coryne mirahilis are most abundant. The 

 medusae of the latter species and of Bougainvillia superciliaris 

 may be found commonly in considerable numbers in the water off the 



