Reviews—Mesozoic and Cenozoic Echinodermata. 277 
be necessary that they should go there with the memoir in pocket as 
a guide. Jee 
Il.—Tuaer Masozorc anp Cenozoic EcurnopErMATA OF THE UNITED 
Srates. By W. B. Crarx and M. W. Twircuett. Washington, 
U.S. Geological Survey, vol. liv, 1915. 4to. pp.-8401, with 
108 plates. . 
‘W\HE marine Mesozoic fauna of North America has hitherto lacked 
detailed description in many directions. This is in part due to 
the relatively poor development of marine deposits of that stage 
(and in particular of the Jurassic), and in part to the consequent 
superior interest attaching to the Palzozoic and Land Vertebrate 
faunas. ‘The volume under review gathers under one cover the 
_ results of various more or less incidental investigations upon the Post- 
Paleozoic Echinoderms of the United States and adds very materially 
to the number of the described species. 
All the orders of Echinoderms whose remains are known from the 
Secondary and Tertiary stages receive attention, but there are not 
many forms described other than Echinoids, and that order alone 
seems to provide types of special interest.' In passing, one might 
protest against the application of a specific name to such obscure casts 
as those figured under the title of Aspidura idahoensis from the Lower 
Trias. That the five-rayed markings on the rock do represent 
Asteroids seems certain, but the fortunate discoverer of a perfect 
specimen would be totally unable to compare it with the type of this 
‘ species’. 
The proportionate numerical strength of the Echinoid faunas of 
the country can be gauged by the fact that 6 pages suffice for 
the Triassic and Jurassic species, while 55 are required for the 
Cretaceous and 113 for the Tertiary. In point of preservation and 
interest, this numerical index is equally reliable. The two Triassic 
species, both Cidaroids and both new, are represented by small 
fragments of the test. Of the eight named Jurassic forms, six are 
Regular Echinoids, of a strikingly European facies, and two might be 
anything. They are referred to Holectypus, and are as likely to 
represent that as any other organism, but to give specific names 
to such material as is figured i is to ‘court confusion. Cidaris taylorensis, 
a new species from the Lower Jurassic, seems, to judge from the 
figure, very problematical. Hither it is a Zetracidaris, or some large- 
tubercled Diademoid. At any rate, the figure does not, as the authors 
state, show two contiguous plates of the same series, 
The Cretaceous Echinoids, and particularly the Regular forms, 
have a surprisingly European, one might almost say British, character, 
nearly all the genera being common to the two ‘countries, and the 
species showing no special differences from those with which 
European Echinologists are familiar. The Irregular forms are mostly 
of a littoral type, and compare equally elosely with similar faunas on 
this side of the Atlantic. The wonderfully prolific stock of the 
Hemiasters seems to have had a flourishing colony in America, but 
some, at least, of the species referred to that genus cannot possibly be 
retained in it. 
