l6 THE AMERICAN ARBACIA 



has been given by Valentin (1841), in a monograph included in 

 L. Agassiz's Monographies d^ £chinodermes ; another of these monographs 

 is that by L, Agassiz on Des Salenies (1838), in which he mentions the 

 genus Arbacia as having been established by Gray. A most interesting 

 book of this period is one referred to previously, by the celebrated 

 marine naturalist, Edward Forbes, entitled A History of the British Star- 

 fishes, and other Animals of the Class Echinodermata (1841), and dedicated 

 to Louis Agassiz. It is a somewhat popular but scientific account of 

 animals belonging to the five main classes of Echinoderms, including 

 several diflferent kinds of British sea urchins. He reckoned that in a 

 moderate sized common British sea urchin, which he calls Echinus 

 sphera {E. esculentus), there are 1,860 suckers, and twice that number 

 of pores (3,720) and about 600 plates "all dove-tailing together with 

 the greatest nicety and regularity, bearing on their surfaces above 

 4,000 spines, each spine perfect in itself, and of a complicated structure, 

 and having a free movement on its socket. Truly the skill of the Great 

 Architect of Nature is not less displayed in the construction of a sea- 

 urchin than in the building up of a world!" (p. 153). Especially inter- 

 esting are the many woodcuts, some of anatomical features, some of 

 scenes, and some imaginative; one of these has been reproduced in the 

 present Monograph as Fig. i. 



The great Swiss naturalist, Louis Agassiz (1807-1873) made im- 

 portant contributions to our knowledge of the Echinoids, both living 

 and fossil, his work being followed by that of his son Alexander Agassiz 

 (1835-1910). The late R. T.Jackson (1861-1948) published in 1912 

 an important volume on the Phylogeny of the Echini and in 1927 Studies 

 of Arbacia punctulata and Allies, a detailed study of the variation of the 

 skeletal parts. 



d. Modern 



The two recent authorities on living sea urchins are the late Danish 

 investigator, Th. Mortensen (i 868-1 951) and the late American in- 

 vestigator, Hubert Lyman Clark (i 870-1 947). The large Monograph of 

 the Echinoidea by Mortensen (i 928-1 951), consisting of 16 quarto vo- 

 lumes of text and plates and an index, was completed just before his 

 death. It is a monumental piece of work devoted to the Echinoidea and 

 a masterpiece of completeness and accuracy. It contains an excellent 

 and very comprehensive account of Arbacia punctulata and its relatives 

 (referred to here as M II: 529-580, Mortensen, vol. II, p. 529-580). 

 These two eminent authorities are in general harmonious, but disagree 

 on a few points of classification and relationships, e.g., Diadema and 



