XII. 
NEW AMERICAN PLATYRRHACID.^. 
The genus Platyrrhacus was based by C. L. Koch on a Brazilian 
species, Polydesmus scaber Perty, or at least on a specimen so deter- 
mined, and described as being slightly convex, densely granulate, 
and with a row of distinct, pearl-like tubercles along the posterior 
margin of each segment. There are said to be two other rows of 
somewhat smaller tubercles placed wider apart. Although the carinae 
are said to be strongly toothed, they appear from the plate that the 
teeth are broad and rounded. After studying the description in con- 
nection with that of another American species described by Koch, 
Platy 7 rhacus riifipes, the opinion has been gained that it would not 
be safe to identify it, even generically, with any of the material which 
has come into my hands for study. 
The genera Stenonia and Stosatea Gray, having had no types as- 
signed to them by their author, remained nomina nuda and can be 
neglected, as Gray himself did in the preparation of a list of the 
Myriapoda of the British Museum (1844), a paper overlooked or mis- 
placed in the bibliographies of Latzel, Daday and Silvestri. If we 
accept for Stenonia a type proposed by a later writer * it must be 
Polydesmus dentatus (Olivier), a species not known to Gray, a result 
certainly not in the interest of either justice or clearness. In the 
past no rule has been consistently followed, the name Stenonia having 
been applied to a great number and variety of genera, both American 
and Malayan. When sufficient types and new material have been 
studied, it will be necessary to rehabilitate the genus Platyrrhacus, 
which may supplant one of those proposed below, but Stenonia 
should be allowed to rest in oblivion. 
The number of American genera of Platyrrhacidse is doubtless 
very considerable, representatives of several of which have been 
loaned me by various museums. The impossibility of describing all 
these under one name, and the apparent artificiality of any arrange- 
ment which does not take into account a wide complex of the charac- 
ters of a series of related forms, are my excuse for proposing the new 
genera whose diagnoses are arranged in the following table : 
Dorsum strongly convex, the carinse strongly decurved in the direction of 
the dorsal arch; carinae of segment 19 distinctly pointed; last segment broadly 
*Gervais, Apteres IV, p. 95, 1847. 
Brandtia, p. 51. 
