46 NATURAL SCIENCE. July, 



suggested by Agassiz that " the immense triangular and curved 

 spines thus formed served to raise the test, as it were on stilts, and 

 enabled the sea-urchin to move with considerable rapidity." 



Among other interesting discoveries may be mentioned Porocidavis 

 elegans, with its curved actinal spines and its long, smooth, primary 

 spines ; and Salenia hastigera, the fourth recent species of a genus well 

 known in the Jurassic and Cretaceous rocks, and always held of great 

 morphological importance owing to the large size of the plates in its 

 apical system. F. A. Bather. 



The collection of Asteroidea has been stated to be one of the 

 most important made during the voyage of the " Challenger " ; it was 

 unquestionably the most important contribution to this group of 

 animals that had ever been made. Representatives were obtained of 

 more than three-fourths (77-5 per cent.) of the previously known types 

 of starfishes ; and, in addition to these, the collection contained 184 

 new species and twelve new varieties, which furnished the types of 

 thirty-four new genera and four new sub-genera (five of the genera 

 and two sub-genera being, however, based on types of which one or 

 more representatives had been previously known). 



The special interest of the collection may be said to centre in 

 the large number of forms obtained from the Abyssal zone, which has 

 practically opened a new chapter in the history of the Asteroidea. 

 The archaic characters of many of these are highly remarkable, and 

 throw important light not only on the relationship of numerous 

 existing forms and upon the classification of the group as a whole, 

 but upon the systematic position of many of the extinct members of 

 the class. 



One hundred and 'nine species and varieties were obtained from 

 the Abyssal zone {i.e., from depths greater than 500 fathoms), all 

 except four of which were discovered by the "Challenger." These 

 represented thirty-five genera, all but sixteen of which were 

 discovered by the " Challenger." Twenty-six genera of starfishes 

 were found living in depths greater than 1,000 fathoms, and all but 

 eight of these were discovered by the " Challenger." 



The Abyssal zone has furnished the following new genera : — 

 Paravchastev, Dytaster, LoncJiotaster, and Aphroditaster, in the Archas- 

 teridae. Porccllanaster, Styvacaster, Hyphalastev, and TJioracaster, con- 

 stituting the Porcellanasteridae, a family wholly due to the " Chal- 

 lenger." Pkoxaster, in the Astropectinidae. Chitonaster, Nymphaster, 

 and Paragonaster, in the Pentagonasteridae. Cnemidaster, in the 

 Zoroasteridae, and Neomorphaster, in the Stichasteridae. Marsipaster, 

 Benthaster, and Pythonaster, in the Pterasteridae — the latter being, 

 perhaps, one of the most remarkable types obtained during the 

 expedition (PI. x.. Fig. 2). To the Brisingids the "Challenger" 

 added a number of species, together with the new genus Colpaster. 



By the discovery of this large series of forms, living under 



