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BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. VOL. 2. NO! 1. 
ficulty in determining the species. Having in mind the beautiful 
ilhistrations in Hall and Simpson's great work, and the number of 
trained paleontologists who had been over the same ground and 
given the results of their labors in the description of a large num- 
ber of distinct species, the writer started in on the work of identifi- 
cation with a cheerful confidence which was all too soon over- 
thrown. The elaborate descriptions and elegant drawings, which 
seem so plain on their face, give no idea of the astonishing varia- 
tions and obscurities presented by the specimens themselves. 
Quite a number of the species collected have certainly never been 
described: and among the others there are such variations in size 
and shape of apertures, height and obliquity of p-^ristomes, as well 
as in the plainness of vesicular openings, appearance of maculae 
and monticules and character of intei-apertural surface generally, 
that the labor, in spite of its fascination, has been unexpectedly 
great. Hall and Simpson's diagnoses show the artificiality of- their 
distinction between the genera Lichenalia and Fistnlipora and this 
is further emphasized by the confusion into which they themselves 
have sometimes fallen, as shown in cross-references in which a 
species is sometimes referred to one genus and sometimes to the 
other. The distinction which they make, based upon the presence 
or absence of superficial openings of the interapertural vesicles, 
cannot be maintained. But Ulrich's distinction between Fistuli- 
pora and Pinacotrypa, depending upon the presence in the latter 
of tubular mesopores in the place of the vesicular structure of the 
former, is not entirely free from the charge of arbitrariness, as 
there seem to be all degrees of gradation between these two types, 
.tickles and Rassler, the latest authorities, show a noticeable lack 
of confidence in deciding between the two genera. Tn addition 
to all these difficulties it is clear that Hall and .Simpson have not 
examined Rominger's and Nicholson's types and have added to 
the confusion by the unnecessary introduction of synonyms. Even 
the genera Pinacofrypa and Lioclcma do not always show a clear 
line of separation, although they have been placed in different 
families and even different suborders. The divergence between 
such forms as Piiiacotrypa scrobiciilafa, P. iinilinea. P. hemi- 
spherica, Lioclema spheroidcmn, L. conferfipornm and L. se- 
gregatum, seems like a very gradual one and would indicate a 
tolerably close relationship. 
Certain groups of species are clearly distinguishable, among 
them the following : 
Pinacofrypa operciilata-stcllata-ninhilicata-variopora; P. clc- 
gans-pl ana-pro por oides-scr ohicnhita-scrrnlata ; Fistnlipora tri- 
faria-vcsicnlata; F. coUicnlata-cultcUata-longimacnla-triangnlaris ; 
