MOLLUSCS. 319 



Limax, as shown in Fig. 348 on a preceding page. In the principal genus, Arion, 

 there is a triangular pore at the upper posterior part of the body, which readily sep- 

 arates it from Liniax. The only spe- 

 cies in the United States which un- 

 doubtedly belongs to this genus is 

 Arion fuscus, which has been intro- 

 duced from Europe into Boston, where 



a colony has existed for many years. ma.m.-Anonfus^s. 



It lives in gardens, and occasionally 



strays into cellars and other dark places. It is not known elsewhere in America. 

 In Europe it is a common species, and its eggs are said to be phosphorescent, shining 

 in the dark for several days after being laid. In color this sjDecies is whitish or gray- 

 ish, sometimes tinged with brown. It reaches a length of about two inches. 



Three other genera of Arioninse, Ariolimax, Prophysaon, and Hemphillia, are 

 found on the Pacific coast. 



The last sub-family, the Limacinse, embraces the largest proportion of the slugs, 

 the typical genus, Limax, containing about one hundred species. This is the only 

 genus represented in the United States, where, besides our native species, we have 

 several introduced from Europe. Our largest species, Limax maximus, is one of these 

 immigrants, which has been found in several places in America. Its rich brown or 

 black spots and stripes upon an ashy or light brown groundwork make it a conspicuous 

 form. 



Another imported species is X. Jlavus, bi-own or brownish in color, with lighter 

 spots. This is more common than X. maximiis, and is found in various Atlantic cities 



from Boston to Charleston. It lives in cel- 

 3^.4^ ' iJ^^^^^S^^ 1^''^ ^^d ill gardens, preferring the former. 



Still more common is the smaller X. agres- 

 iis, which is also an introduced form. It 

 is smaller than the others, and is extremely 

 variable in color. It lays more eggs than 

 FIG. 392. -Zimax flav^ *''® ^wo species mentioned, and the period 



of reproduction appears to last through the 

 warmer months of the year. Our native Limax campestris is very common, and is 

 found in the woods and the open fields, along the sides of the roads and in gardens. 

 It is brownish gray or amber colored, and is smaller than the other species men- 

 tioned. The eggs are i-ather numerous and transparent, and are laid under leaves or 

 in moist earth. Di-. E. L. Mark has studied the earlier stages of the development of 

 .this species ; a later stage is shown in Fig. 348. 



Another genus, Phosphorax, which is very imjaerfectly known, comes from the 

 Cape Verdes. The only species is said to be phosphorescent, as is indicated by both 

 its generic and specific names (P. noctilucens). 



Ordee III. — ZYGOBRANCHIA. 



All of the gasteropods which follow belong to the Streptoneurous group, the 

 characters of which were detailed on a preceding page. In the first division, the 

 Zygobranchia, the torsion of the body has not been accompanied by an atrophy or 

 disappearance of the organs of the primitive left side, and we thus have the gills and 



