THE MOUNT DESERT EEGION 167 



the eyebrows in certain quarters, but in tliis Region there is 

 no difference between the two forms. They occur together in- 

 discriminately where rocks and eel-grass are together, and the 

 alveus form, which is supposed to live on eel-grass, occurs 

 on all rocks and the testudinalis on the eel-grass. To test this 

 out the writer took 55 specimens on eel-grass and 25 from a 

 rock surrounded by the eel-grass. Of those from the rock, 

 the largest of which, varying from 11 to 17 mm. in length, 

 are typical testudinalis, while the 12 smaller ones, varying 

 from 5 to 10 mm. in length, approach the form alveus. Among 

 those from the eel-grass, the 5 largest are typical testudinal, 

 the largest measuring 11 mm. in width and 15 mm. in length ; 

 about 20 would be considered the form alveus, the largest 

 having a width of 77 mm. and a length of 12 mm. Thirty were 

 intermediate, completely bridging the two forms. These forms 

 were checked over by C. W. Johnson and mentioned in Nau- 

 tilus. One may go to the Narrows at low tide today and find 

 the above conditions, with thousands of individuals readily 

 accessible to prove the above observation. 



Phylum MOLLUSCA 



AMPHINEURA 

 POLYPLACOPHORA 



Lepidopleuridae 

 Hanleya Gray 

 Hanleya mendicaria Mighels and Adams 



Ischnochitonidae 

 ToNiCELLA Carpenter 

 ToxiCELLA MARMOREA (Fabricius) 



Trachydermon Carpenter 



Track YDERMON albus (Linne) 

 Trachydermon ruber (Linne) 



