OF CONCHOLOGY. 219 



Barbara Island, about 28 miles west of the north end of 

 Catalina, is entirely basaltic, but has a surface soil chiefly com- 

 posed of the remains of seals, birds, etc., which are still numer- 

 ous there, but formerly much more so, and have supplied the 

 lime necessary for molluscan shells. The vegetation is chiefly 

 of Cacti and other succulent plants. Over the whole surface, 

 but chiefly the south-east slope, are scattered myriads of the 

 shells of H. Tryoni, Newc, and on the latter part great numbers' 

 of H. facta, Newc, many of both living, but even in May aesti- 

 vating, sticking to plants, to each other, and some of the former 

 three or four feet high on shrubs. 



Fossil specimens of both show that they have inhabited the 

 island for a long time, and that while the former were once a 

 third smaller, and often subangulate, the latter were twice as 

 large as now, but exactly similar in form and number of whorls.* 



Near the head of a deep, narrow canon facing the south-east, 

 where in the rainy season there is a small spring (the only water 

 on the island), among loose rocks I found Patula Durantii not 

 uncommon, and all the specimens of Binneya noto.bilis yet dis- 

 covered. The latter was sestivating under roots or stones, en- 

 closed in its white, tough, membraneous envelope, to which the 

 shell formed a kind of lid.f Only three living and eighteen dead 

 shells occurred. (See Proc. Cal. Acad., iii. 1, 63, 1863.) It is 

 not unlikely that this interesting species may yet be found on 

 the main land, especially in the mountains west of Los Angeles, 

 which form Points Duma and Mogu, lat. 34°. These are well 

 wooded and watered, therefore suitable for land shells, but I do 

 not know that any collector has explored them near the coast. 



Nicolas Island lies a little south of west of Barbara island, 

 and distant 2? miles. It has an elevation of about 600 feet, is 



* The subangulated and carinate forms of Helicoids seem nearly always 

 connected with mountains where shaly or other flat rocks full of crevices 

 are the chief formation, and trees scarce. They appear to be '* Dar- 

 winian" mollifications of the rounded forms. Thus •' lapicicla" of Europe 

 got its name, and as in other cases there seems to be always a corre- 

 sponding rounded form, may not ru/escens, Penn., be the congener of 

 lapicicla ? 



From this fossil form of Tryoni we may argue that the island is a 

 remnant of a former shaly mountain, which has either sunk or washed 

 away, and that the climate was then somewhat different. The suban- 

 gulated form is always a mark of arrested development, the young of most 

 species [Tryoni included) being subangulated. It is certainly not a 

 specific character. 



t In the colored copies of his monograph Mr. Tryon has erroneously 

 colored the membrane. In thin specimens the viscera of the animal can 

 be seen through the shell only. 



