1898.] NATURAL SCIENCES OF PHILADELPHIA. 237 



Genital system (PI. XII, figs. 44-48) having a well developed 

 penis with terminal retractor and epiphallus, lumen with plicate 

 walls (fig. 45), and a large apical penis papilla (figs. 45, 46). 

 Atrium hearing a vermiform appendicula with swollen base (fig. 44 

 ap ; fig. 47, ap). Spermatheca borne on a short, basally swollen duct. 

 Spermatophores (fig. 43, x H) cbitinous, elongate, with flagellum- 

 like extension at one end. Ovotestis separated from albumen gland, 

 lying on the right side under G 3 , to the right of posterior end of 

 stomach (PI. XI, fig. 33, ot.). 



Muscle system (PI. XIV, fig. 71) Ariolimacine in having the re- 

 tractors converging posteriorly, their proximal insertions contigu- 

 ous ; buccal retractor deeply bifurcate. No " retensor." Penis 

 retractor short, broad, inserted in the left anterior portion of the 

 lung floor or diaphragm (fig. 71, r.p.). 



Lung as usual ; kidney very large (PI. XV, fig. 77, k). Only the 

 ventricle exposed. 



Distribution : Middle portion of California, in the counties lying 

 near and below San Francisco Bay, west of the Sierra Nevada. 



Externally H.espterarion is like Ariolimax and Aphallarion except 

 in the structure of the caudal pore, which is a deep, open pit in this 

 genus, while in the others it is filled by a mass of spongy tissue. 

 The jaw, teeth, intestine, pallial region and musculature of the 

 three genera are practically identical in their main features, except 

 that Hesperarion totally lacks a " retensor" muscle. 



In the genitalia are found further important differences. The 

 ovotestis is not packed adjacent to the albumen gland anteriorly, as 

 in Ariolimax and Aphallarion, but is carried back to a more pos- 

 terior position among the hind loops of the intestine, and surrounded 

 by the liver (PI. XI, fig. 33, ot.). The penis, externally similiar 

 to that of Ariolimax, is of the usual simple structure, not invagi- 

 nated, and the atrium bears an enigmatic organ of unknown func- 

 tion, our ignorance of which is veiled behind the term "appendic- 

 ula." 12 This is wanting in other Arionidce with the exception of 

 Binneya, the most primitive genus of the family. 



The species of Hesperarion are dimorphic, like Ariolimax colum- 

 bianus, having a spotted and an immaculate form. 



12 This convenient term was first used by Dr. von Ihering in his " Morpholo- 

 gie und Systematik des Genitalapparates von Helix." The appendicula in- 

 serted low on the vagina or on the atrium is not homologous with the elon- 

 gated sack found in Panda, Strophocheilus, etc., associated with the spermatheca. 

 The latter probably serves the purpose of an accessory spermatheca. 



