x OXYSTYLA. 



(p). 56, fig. 58). Towards the sides a small ectocone gradually makes 

 its appearance, becoming somewhat conspicuous on the outer mar- 

 ginal teeth, and the entocone is usually indicated by a slight notch 

 in the cusp (pi. 56, fig. 57, 53). 



This type of teeth resembles the Zaplagius type superficially, but 

 differs fundamentally in that the ectocone is united with the meso- 

 cone, while in Zaplugius it is always distinct. 



The broad, shovel-shaped type of cusp described above is some- 

 times replaced on the median and a few adjacent lateral teeth by long, 

 lanceolate cusps. This modification has been observed in 1 Agnus 

 virgineus, L. (Hemibulinius} maynijicus, Orthalicus sultana and atra- 

 mentarius, Oxystyla feriissaci and princeps, though some individuals 

 of the latter have the normal type of teeth. In my opinion, these 

 lanceolate teeth have been modified from the rounded type, second- 

 arily assuming a pointed shape ; this view being based upon the gen- 

 eral law of tooth-changes set forth in Vol. IX, p. xiii. The species 

 of various genera possessing such teeth are unrelated, and have ac- 

 quired them clearly by a parallel process. In Oxystyln fjrinceps, as 

 Strebel & Pfeffer have shown, the form of the cusps is not a constant 

 specific character. The same is true of Liyitus. 



Genus OXYSTYLA Schliiter, 1838. 



Vol. xii, p. 101. Synonyms are Zebra SHUTTL., 1856, Ortaliclms 

 Martens, 1893, and Orthaliciis of writers on North American species. 



While the other genera are restricted in distribution, Oxystyla ex- 

 tends throughout the tropical and subtropical regions of both 

 Americas, though in South America the species are more numerous 

 and diversified. 



The kidney and lung (pi. 53, fig. 34, 0. undata jama/censis), re- 

 tractor muscles (pi. 54, fig. 36, 0. u. jamaicensis) and jaw have 

 been treated of under the subfamily head. The radula has about 

 100.1.100 teeth in 0. u. jamaicensis (pi. 56, figs. 57, 58), the cusps 

 being broad and rounded as usual. Most of the species investigated 

 have similar teeth. In some forms of 0. princeps and 0. ferussaci 

 (pi. 59, fig. 7, after Strebel) the middle and some adjacent lateral 

 teeth have lanceolate cusps. When this is the case, the number of 

 teeth so modified was found to be unequal on the two sides. 



The jaw (pi. 60, fig. 18, O.longa) has been described above. The 

 number of plaits varies in different species. 



