HISTORICAL SKETCH. XV11 



The musculature of the genitalia is often a character of some value. 

 The penis retractor may be inserted either on the penis itself, or on 

 the epiphallus ; and in a few cases it is split, having a double or triple 

 insertion. Distally it is attached normally to the lung floor, but in 

 a few cases to the vagina, or to the main columellar retractor of 

 foot and buccal mass. In a few groups the penis retractor is absent, 

 The vagina in some cases is attached to the adjacent body wall by a 

 broad band-like muscle. The dart sack has no retractor, but in 

 certain genera its apex is connected with the vagina. The retractor 

 of the right eye-peduncle in most genera passes between the penis 

 and vagina; but in a few it passes to the left of the penis. These 

 myologic features are of considerable importance in classification; 

 and the variation in the distal insertion of the penis retractor in some 

 forms, as well as the abnormal position of the eye-retractor in others, 

 are difficult to explain. 



II. HISTORICAL SKETCH OF THE CLASSIFICATION or HELICKS. 



Five epochs may conveniently be recognized in the taxonomic 

 history of land mollusks. I, Linupean epoch; II, Lamarckiau 

 epoch; III, Ferussaciau, IV, Beckian, V, Albers-Martensian ; each 

 of these being initiated by the appearance of some work largely re- 

 modelling the system of classification. 



I, 1758-1799. The LINN/EAN EPOCH was characterized by the 

 wide limits and heterogenous contents of its genera, although 

 in a broad sense most of them have proved to be natural groups. 

 Linnseus himself and his successors in Germany, France and Eng- 

 land until the time of Lamarck, are the exponents of this period. 



II, 1799-181,9. LAMARCKIAN EPOCH. The genus Helix of 

 Linnrcus was much restricted about the beginning of the present 

 century by the segregation of its most diverse elements by LAMARCK 

 and DRAPARNAUD; the Limnophila, Clausilia, Pupa, Succinea, 

 .Achatina, etc. being removed to form distinct genera. Within the 

 group of forms retained in Helix, but few divisions were made, and 

 such genera as were instituted during this epoch were rnainlv based 

 on one or a few peculiar species, no attempt being made to classify 

 the entire series. Fischer de Waldheim (about 1808), Mont fort 

 (1810), Schumacher (1817) are the principal contributors to this 

 literature. 



III, 1819-1837. FERUSSACIAN EPOCH. The Tableaux Systema- 

 tique de la Famille des Limacons presented the first consistent attempt 



ii 



