THE SEA-SLUGS. 265 



occur all round the coast, though their relative abundance varies 

 greatly. In the West and South-west as indeed everywhere to a 

 greater or less extent other species occur between tide-marks, but 

 the forms mentioned may be sufficient to afford an insight into the 

 chief modifications of external form in the Nudibranchs. Certain of 

 the species of Doris are especially widely distributed and common. I 

 have found singularly fine specimens of D. tuberculata in abundance 

 between tide-marks, at such widely separated localities as Alnmouth 

 and Aberystwyth. Many of the Nudibranchs, indeed, seem to be as 

 universally distributed around our coasts as such familiar forms as 

 the common shore crab, the mussel, cockle, shrimp, periwinkle, but 

 in most cases the sea-slugs are less likely to be noticed than these. 



