180 
ASPIDIACE^. 
expected) is a slight indication discoverable of a iheciferous vein 
being continued to the edge of the pinnule ; but in this the ap- 
pearance is very different to the decided character observable in 
P. lobatwm^ ” ^ 
Mr. Thwaites has most obligingly sent me his series of spe- 
cimens illustrating the observations above recorded : they are 
accompanied by the following note. 
I have just been re-examining the specimens upon which I 
satisfied myself of the validity of the characters 1 gave as dis- 
tinguishing the two kinds, and have looked over some other 
specimens received from correspondents ; and I remain as con- 
vinced as ever that the said characters are sufficient to discrimi- 
nate the two, notwithstanding exceptions occur more frequently 
than I at first observed, — some of the pinnules of P. aculeatum^ 
in which the sori are distant from the margin, resembling those 
of lobatum^ and some of the smaller pinnules of P. lohatum hav- 
ing the characters of aculeatum: but these appear to me as un- 
common exceptions, and not materially to diminish the value of 
the character I pointed out.” 
As regards this character, it will perhaps be sufficient for me 
to say, that I have most thoroughly examined it without feeling 
convinced of its value. I beg to refer my readers to fig. h, at 
page 167, as an illustration of the abbreviated vein to which Mr. 
Thwaites alludes ; this figure was drawn from a pinna of the 
Snowdon plant, and was published nearly two years anterior to 
Mr. Thwaites’ observations. Now the Snowdon plant is the true 
Lonchitis, according to all the evidence offered by the works 
and herbaria of Linneus and Sir J. E. Smith ; and this form of 
Lonchitis certainly has the abbreviated vein. Thus it would 
appear that Lonchitis corresponds in this character with the 
more divided form of angulare^ while it equally recedes from its 
more immediate congener known as lohatum^ a fact rather op- 
posed to the reception of this character as a safe diagnostic. 
But even laying aside this seeming objection, and admitting the 
value of the character as far as the extreme forms are concerned, 
it will be seen, that even according to Mr. Thwaites’ own ac- 
* Phytologist, 112. 
