270 
PYCXOGLOSSATE AND ZEUGOGLOSSATE TEETH. 
The PrCNOGLOSSA ( ttvkvo ^, crowded ; y/\wcro-a, tongue) may he con- 
sidered as the typical dentition of the Puhnouates generally and of the 
Helices in particular. It is characterized by the enormous number and 
close arrangement of the individual teeth, which resemble mosaic work 
in their compact methodical arrangement. The mid-tooth is usually 
tritidly retlected with the mesocone much the longest, while the 
laterals and marginals are more or less asymmetrical moditications of 
the type of the central tooth, each tooth becoming more numerously 
denticulate and with wider base as the margin is approached. The 
transverse rows are usually gently curved, ai)proaching the median 
line at almost right angles. Tliis gradual change in direction gives 
rise to intermediate or transitional teeth, connecting impercei)tibly the 
Fid. 540. — Representative teeth of hnlf a transverse row of teetli o Helix nsf>ersa Mull., hii^lily 
niagnil'ied, collected by Dr. ScharlT near Dublin. 
The numerals appended to the figures of ihe teeth indicate their position in the tran.sverse row. 
lateral and marginal series, ilellv aspersa is a typical example of 
this group, and its i)eculiarities can he exinessed l)y the formula : 
4- 1 + x Uo=12,(; 1 5, 
showing that species to possess 12,01.7 teeth, contained in 1-1.7 trans- 
verse rows, each containing a central tooth, bearing 3 cusps, 20 
laterals at each siile with 2 cusps, and 33 marginals and transitional 
teeth, with 3 — 4 cusps each. 
The Zel’Goglossa paired; y/Vdio-cra, tongue), of which 
J^hinorbh corneus may be taken as an example, are distinguished by 
the paired or hitid cusps to the teeth composing the median longi- 
Fii;. .m. — Representative teetli from a transverse row of the oilontophore of Planorhh 
roivn-Ki (1..), hii^hly magniriei.1, collected at Northampton by .Mr. L. E. .\dams, 11. A., prepared by 
.Mr. J. W. Neville. 
The mimerals aiipended to the figures of the teeth indicate their position in the transverse row. 
tudinal row ; the laterals being also hicuspidate and the marginals 
e.xhihiting the comh-like teeth of the Acanthoglo.s.sate tyjie. The 
formula of Pldnorbh corneus may be written as : 
_|. s + i + s + X 200=1 3,400. 
