296 ECHINUS NORVEGICUS. 



(see PL VIII. f. 29), while in Psaramechinus the pores frequently remain 

 vertical so long that we might be tempted, as has been frequently the case 

 in allied fossil species, to retain the adult in the genus Arbacia Agass. non 

 Gray, from the impossibility of stating confidently whether the pores were 

 arranged in arcs of three pairs or not. 



Echinus norvegicus 



! Echinus norvegicus Dub. o. Koken, 1844. Skand. Echin. 



PL VI". f. 4. 



Test Hat, slightly conical, depressed. Ahactinal system prominent, com- 

 pact, raised above level of test. Anal system small, genital plates huge, with 

 large genital openings, and prominent secondary tubercles on part near anal 

 edge. Two principal vertical rows of primary tubercles in ambulacra! and 

 interambulacral space, with two shorter vertical rows of larger secondaries 

 extending from actinostome to ambitus, in interambulacral space, on each 

 side of primary row, and from ten to twelve secondaries on each plate, with 

 intermediate spaces filled by miliaries. Ambulacral space narrow, plates well 

 covered by secondary and miliary tubercles except along median line near 

 abactinal region where bare as well as in the interambulacral median space. 

 Mouth rather larger than in other species of Echinus of its size. E. norvegicus, 

 like E. elegans, is Battened below, with the actinostome somewhat depressed. 

 Primary spines straw-colored, long, sharp, tapering ; secondaries, same color, 

 attaining about one half the diameter of the test. 



The variations of species of true Echinus are very considerable, the spe- 

 cies recognized are by no means discriminated with the accuracy which is 

 required, and the differences of opinion prevailing respecting the number of 

 species of this genus, as is readily seen by examining the >S\ - nonyinie Lists of 

 various writers, show how much remains to be done. The remarkable uni- 

 formity in appearance of the specimens of the allied species of E. elegans. nor- 

 vegicus, Flemingii, melo, and the absence of complete series of different sizes 

 of the different forms, seems to make it impossible at present to characterize 

 these species with great accuracy; and I give with great hesitancy such 

 differences as I have noticed which appear constant, stating at the same time 

 that E. Flemingii, E. elegans, and E. norvegicus may yet turn out identical 

 species, as well as E. gracilis and E. melo, though the material at command 

 in the different Museums does not at present justify such a position. 



I had not, when writing the Preliminary Report, seen a good series of 



