200 Review of Recent Geological Literature . 
If one gives this work no more than a casual glance he is impressed 
with the exactness of the science of microscopic petrography, and with 
the patient and long labor that the authors have expended on the study of 
minerals in thin sections. No young man can enter upon and prosecute 
this study as a pastime. He who carries it to completion receives one of 
the most severe of mental trainings, and he gets an insight into some of 
the exact methods of nature as inspiring to the devout worker as those of 
astronomy. This work will contribute, as remarked by M. F. Fouqud, 
very largely to the extension of the science of the rocks. It is by works 
of this kind that micrographic methods will finally win the place that is 
due them in the University programs and in the instruction given in th© 
higher schools. It is a companion, although later to appear, and a natural 
complement, of Mineralogie Micrographic , by Fouqu6 and L6vy published 
in 1879. 
Discovery of the Ventral Structure of Taxocrinus and Haplocrinus, and 
Consequent Modifications in the classification of the Crinoidea. By Charles 
Wachsmuth and Frank Springer. From the Proc. Acad. Nat. 8ci., 
Philadelphia, November 27, 1888. This contribution to crinoid morph¬ 
ology may justly be regarded as one of the most important ever chronicled; 
and its effect upon the present systematic arrangement of the crinoids w ill 
be to demand a complete reclassification of the order. The memoir is th© 
ultimatum of a long and heated controversy between the authors and Dr. 
P. Herbert Carpenter, the eminent English authority on Crinoids. Both 
found themselves partly in the right; partly in error. But it is indeed 
gratifyingto learn that the views of each are now practically in harmony; 
and that the final result of the discussion, extending over a long period of 
years, has been to place the classification of the Crinoidea upon a firmer 
and more rational basis than even the most sanguine could anticipate a 
decade ago. 
The immediate occasion for the present publication was the discovery 
of the non-existence of a central plate in the ventral side of Haplocrinus; 
and of the presence of an open mouth in Taxocrinus. The so-called 
central plate in Haplocrinus is now proved satisfactorily to be a lingui- 
form extension of the posterior interradial—or as it must now be denomi¬ 
nated the posterior oral—instead of being completely separated suturally, 
as suggested in the Revision of the Paleeocrinoidea, part iii. Another 
structural feature in the calyx of Haplocrinus , as disclosed by th8 present 
investigation, is the location of the anal opening. 
The presence, in Taxocrinus , and probably in the Ichthyocrinidac gen¬ 
erally, of an open mouth, surrounded by irregular plates, in number 
and arrangement similaf to the hitherto known “central” and four “proxi¬ 
mal” plates, presents suggestions of much significance as effecting the 
entire classification of the crinoids. The import of the recent discovery 
is: (1) that structurally the older and later crinoids are not separated as 
widely as heretofore regard d; (2) that there is no substantiation, as Messrs. 
Wachsmuth and Springer supposed, for considering the universal presence 
of interradials in the older crinoids; nor for regarding the mouth in all 
