226 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Paradoxides spinosus W. B. Rogers, Geol. Penn., 1858, 2, p. 816, fig. 590. 
Barrande, Bull. Soc. geol. France, 1860, 17, p. 551; Proc. Boston soe. nat. 
hist., 1860, 7, p. 369. 
This species has often been described and is too well known to re- 
quire any formal description here; but I wish to emphasize certain 
features which, while now recognized, really have more importance 
than has previously been ascribed to them. As seen by the references 
cited above, Barrande considered P. harlani as identical with the 
Bohemian P. spinosus. This identification was immediately con- 
troverted by Ordway, and later writers have not accepted it; but of 
the two really vital differences of P. harlanza from P. spinosus and most 
other species, only one has ever received attention. Ford (Amer. 
journ. sci., 1881, ser. 3, 22, p. 250) has called attention to the fact that 
the species of Paradoxides may be divided into two groups, in one of 
which the second segment of the thorax is always prolonged beyond 
the others, while in the other group the second segment is in no way 
distinguishable from the others. To the first group belong the Bo- 
hemian and South European species, while the Scandinavian, British, 
and American forms belong to the second group. Paradowides 
spinosus has the second segment extended, while P. harlani has not. 
The second feature in which P. harlanz differs from other species, 
and one which makes it almost unique, is the wide, depressed brim 
at the anterior end of the cranidium. Of the forty-six recognizable 
species of Paradoxides whose cranidium is known, only four, Para- 
doxides bennetti Salter, P. groomi Lapworth, P. regina Matthew, and 
P. harlant Green have a rimless brim (though there is a possible fifth, 
P. brachyrhachis Linnarsson). Of these, only two, P. harlani and 
P. regina have a wide brim in front of the glabella. All other species 
of Paradoxides described from adult specimens have the glabella 
reaching nearly or quite to the anterior margin. 
Among the numerous cranidia obtained from the Paradoxides beds 
at Braintree, there are some of the smaller ones which have a rim on 
the front of the cranidium, and the front of the glabella almost reaches 
the rim. These specimens have been considered by previous writers 
to be the young of P. harlani, and it was believed that in later stages 
of growth the anterior part of the cranidium became widened and 
flattened. Specimens recently obtained by the writer from Mr. 
Hayward’s collection show that this could not have been the case, for 
there are specimens of the broad brimmed type which are of the same 
size or smaller than some of those showing the rim. The rimmed 
