Schuchert — Jackson on the Phytogeny of the Echini. 251 



Art. XXIII. — Jackson on the Phytogeny of the Echini •* A 

 synopsis by Charles Schuchert. 



In this monumental monograph are established the phylo- 



• geny and classification of the Echini, including young and 



adult, fossil and living types, and " based on the sums of the 



characters and not on single characters." The volume also 



contains a revision of all Paleozoic Echini. 



The splendid and fully illustrated work is dedicated to the 

 great echinologist, Alexander Agassiz, and to Alpheus Hyatt, 

 " my beloved master and friend, whose principles of research 

 are the keynote of this memoir." Hyatt's principles are the 

 stages in development, senescence, acceleration, and parallel- 

 ism, and it has been Jackson's constant aim to compare these 

 stages with the characters of more or less closely associated 

 types. 



Jackson began to study Echini in 1896 and during the past 

 seven years he has devoted most of his time to a detailed study 

 of the species and genera of this class of Eehinoderma. He 

 assembled in his private collection more than 40,000 specimens 

 of Recent and Mesozoic Echini in all stages of growth, actually 

 studying more than 50,000 specimens, so that he might 

 thoroughly understand the Paleozoic species and their phylo- 

 genetic relations to the later forms. That he has succeeded 

 the volume bears abundant evidence, for no class of inverte- 

 brates, as a class, has been wrought out with more care and 

 philosophic insight. 



One of the most important features of the work is a new 

 method of determining ontogenetic stages of growth by noting 

 how the plates are introduced ventral ly, and in the localized 

 stages among the plates dorsally. Echini are a particularly 

 good class to study phylogenetically, because they have so 

 many parts, all of which must be taken into consideration. 

 This mass of detail furnishes constant checks and when all are 

 in accord proves the accuracy of the resulting phylogenetic 

 scheme. 



Geological Occurrence. 



Aldrovanus in 1618 was the first to figure a fossil echinoid 

 from the Paleozoic and curiously one of the rarest of species 

 and the oldest geologically, Bothviocidaris globulus. 



The author recognizes 21 genera of Paleozoic Echini and of 

 these but 4 are new to paleontology (Hyattechi?ius, Lovene- 



* Phylogen y of the Echini, with a revision of Palaeozoic species ; by Rob- 

 ert Tracy Jackson. Mem. Boston Soc. Nat. Hist., vii, quarto, 491 pages, 76 

 plates, and 258 text figures, Jan., 1912. 



