a 
16 HYALINIA HELVETICA. 
This proposal to separate our British specimens ot /lyalinit helvetica as 
an independent species is, however, to be earnestly deprecated as adding 
another ill-defined and unsatisfactory species to an already difheult group ; 
a form, too, which shows no real external differences, and is based 
almost solely on slight and insufficient variations in an organ so unstable 
as the radula has been shown to be in the //yalini@, and which render 
this organ an eminently unsuitable one on which to base a new species of 
Euhyalinia, as the species already recognized owing to their closely inti- 
mate relationship and similarity to each other are so difficult to identify 
correctly as to have often led to many serious errors of discrimination 
and record. 
The precise characters upon which the proposed separation is chiefly 
based are described as a slightly larger radula with somewhat less numer- 
ous longitudinal and transverse rows of teeth thereon ; but more especially 
the differeut form of the admedian teeth. It is, however, unfortunate, 
that the distinctions shown are not conclusive or satisfactory, as the teeth 
figured by Mr. Woodward to illustrate the difference between his //. 
rogerst and IT. helvetica are not truly representative, both being more or 
less abnormal examples of the forms to which they are referred, and if 
accurately drawn, aptly illustrate the variability of the teeth and their 
unsuitability taken alone to furnish reliable specific characters. 
Fic. 74.—Representative teeth from the odontophore of IZtrea rogers? B. B. Woodward, x 180 (after 
Woodward). 
The formula of the figured specimen is given as 
114+14+24+14+2+1+4+11x40 = 1,160. 
Fic. 75.—Representative teeth from the odontophore of a topotype of I’itvea helvetica (Blum) from 
Solothurn x 180 (after Woodward). 
The formula of the figured specimen is given as 
a Le 2 2 x4 do. 
The radulze of many British specimens of /7. helvetica from widely distant 
districts have been carefully examined by Messrs. Moss and Boycott, who 
have verified the great variation to which it is subject and as a result of 
their researches regard the species as in this respect not closely homo- 
geneous but in a transitional stage; the variation in the number of the 
transverse rows being found to be from thirty-one to forty-five, and the longi- 
tudinal rows ranging from twenty-five to thirty-two, while the median row 
though most usually presenting a long and well- developed mesocone, very 
frequently has the median cusp truncate and scarcely or not at all pro- 
jecting beyond the adjoining ectocones, resembling in this respect the true 
Hyalinia glabra, in which this peculiarity is a constant and invariable 
feature. 
