PACIFIC COAST SPECIES. 



95 



Inhabits the Pacific Province, on the Pacific coast of the United 

 States, at least from latitude 34° to 49°, as far as now known not east- 

 ward of the Sierra Nevada and Cascade Eanges. 



The genus has affinities with, but is readily distinguished from 

 Umax, Avion, and PropJtysaon. It agrees with Limax in having an 

 internal shelly plate, in the position of its respiratory orifice and its 

 distinct locomotive disk, but it differs in having a caudal mucus pore, 

 a ribbed jaw, quadrate (not aculeate) marginal teeth on the lingual 

 membrane, and in the position of its genital orifice. With Arion it 

 agrees in having a mucus pore, a distinct locomotive disk, a ribbed 

 jaw, in its lingual membrane, and position of the genital orifice; but it 

 differs in the position of its respiratory orifice and its internal shell. 

 With Prophysaon it agrees in having an internal shell, a ribbed jaw, 

 in its lingual membrane; but differs in the position of the genital and 

 respiratory orifices, in its distinct locomotive disk, and caudal mucus 

 pore. From the other shiglike, or semi-sluglike American genera, 

 TebennopJiorus, PalUfera, Binneya, HemphilUa, Veronicella, it is most 

 readily distinguished. 



Jaw thick, slightly arcuate, ends but little attenuated, blunt; low, 

 wide; anterior surface with numerous stout ribs, _J^!!Z^ 



denticulating either margin. The number of ribs 

 varies in the several species, and in different indi- 



Jaw of ArioUmax 



viduals of the same species. Fig. 59, drawn from coiumUanus. 



the true northern A. Columhianus, has 18 ribs; another specimen, sup- 

 posed to be the same species, has about 12. A. Calif ornicus has given 

 13 and 14 ribs. A. nig er has been described by Dr. Cooper with 20, 

 but I found only 8 in one specimen which I refer to that species. In 

 A. RempJiilU there are from 8 to 12; in A. Andersonif there are 13 

 ribs. 



Fig. 498 of p. 279, Land and Freshwater Shells IST. A., I., gives the 

 general arrangement of the teeth upou the lingual membrane. It is 

 drawn from the true northern A. Columbianus. Its general arrange- 

 ment is as in Patula. On Plate V, Fig. E, of Ter. Moll., V, I have 

 given more detailed figures of the dentition of a specimen of this 

 species. It will be seen that the central teeth have a base of attach- 

 ment longer than wide, with expanded lower angles and incurved lower 

 margin ; the upper margin is reflected ; the reflection is large, broad, 

 and has a short, stout median cusp, bearing along, stout cutting point; 

 the side cusps of the reflection are subobsolete, but there are well-de- 



