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DR J. STEPHENSON ON 
various authors—that is, that there is no general agreement as to what the points of 
difference are. It will further appear from the above descriptions, that of the Millport 
specimens included, that these forms, or at any rate P. candidum, are subject to a great 
amount of variation. And it will be seen also that specimens have come under examina- 
tion which unite in themselves characters ascribed to the two forms separately. 
With regard to the first point, it appears from a tabulation of the characters of the 
two species, as given by the several authorities, that the only distinguishing character 
in which all agree is that in P. candidum the head is broader than, in P. flavidum of 
the same width as, the succeeding part of the body ;* even this is not stated directly 
by BUrexrr with regard to flavidum, but it may perhaps be inferred from the fact that 
the head of flavidum is said to be not marked off from the body. 
Thus, with regard to colour, while it is generally agreed that green or yellow, or 
both, are the characteristic colours of candidum, and a pinkish or a rose colour of flavi- 
dum, JouBIN finds red specimens of candidum also. MaclInrosu alone mentions various 
markings on the head of both species. Joupin states that the head is long in favidum, 
and the distance between anterior and posterior eyes greater (‘leurs ganglions sont trés 
allongés comme la téte en général, dont les yeux sont plus distants que dans aucun 
autre Tetrastemma”); Macliytosu finds the eyes arranged in a square in candidum, 
while the interval between anterior and posterior eyes is greater in flavidum; but 
BurGeR makes no distinction between the two forms as regards this feature. Maclyrosx 
alone notes that candidum is of active, flavidum of a more sluggish habit. Differences 
in the relative length of stylet and basis, and in the shape of the basis, have been noted 
only by Bircer. 
To the fact that there is no general agreement as to the distinguishing characters 
of the two forms is to be added the fact that the forms themselves are very variable. 
This may be illustrated by the different colours and combinations of colours assumed, 
especially by P. candidum; Joustn specially notes the variability of this form, and 
gives for it a greater range of colour than other authors; he mentions white, yellow, 
green, and red. The length, again, as given by BUragr, is in the case of P. candidum 
only one-third of that given by Maclytosu, and little more in the case of P. flavidum. 
The size of the eyes, according to BUreErR, is “very small” in both; this is not noted 
by other authors, and was very distinctly not the case in the Millport specimens. With 
regard to the shape of the basis of the stylet in P. candidum, Buresr, as has been 
seen, gives a description which is quite inapplicable to my specimens ; and with regard 
to P. flavidum, while the figure in his Naples monograph shows the basis to be some- 
what dumbbell-shaped, with a constriction in the middle and rounded ends of equal 
size, his description of this structure in the Tverreich runs ‘‘der kegelférmige, kaum in 
der Mitte eingeschniirte Sockel.” .And it has been seen that in my own specimens 
of P. candidum, in addition to well-marked colour differences, the length, the pig- 
* JouBIN has not given full descriptions of these forms ; in points not specified by him he associates himself with 
Maclnvosu, and accordingly is counted as agreeing with this author in such cases, 
