152 



ECHINOIDEA. I. 



Accordingly the species has been taken in considerable numbers and on many localities, and 

 so it would be a remarkable fact, if it had not been taken before by any deep-sea Expedition. It 

 has also been taken, and surely numbers of times; it has only been confounded with other species. 

 I am able to substantiate the following instances: From U. S. Fish Commission (Smithsonian Institu- 

 tion) our museum has received 4 specimens under the name of Echinus norvegicus; they are typical 

 Ech. a/finis. (Albatross. 1884. 39 35' N. L,. 7i24'W. L. 1043 fathoms.) In Challenger s-Echinoidea 

 Ech. norvegicus is mentioned from sts. 46 and 47 (eastern coast of North America, off Cape Cod); it is 

 also Ech. a/finis. (On 31.46 it is taken together with Ech. Alexandri, comp. p. 149). Accordingly there 

 can be no doubt that this species like Ech. Alexandri is found throughout the archibenthal zone of the 

 northern Atlantic, and possibly it is still wider distributed. In Challenger-Echinoidea Echinus acutus 

 is mentioned from st 170, off the Kermadec Islands in the Pacific Ocean. After having examined the 

 specimen from this station in British Museum, I must positively assert that it is no Ech. acutus; on 

 the contrary it agrees with Ech. affinis with regard to the tubercles of the ambulacral areas and the 

 pedicellarise, and I have found no character, by which it might be distinguished from Ech. affinis. 

 Accordingly I must regard it as a rather sure fact that it is Ech. affinis; a more thorough examina- 

 tion will, however, be necessary in order to establish the fact definitively. - - North of the ridges 

 between the Faroe Islands and Iceland, and between Iceland and Greenland it has not been found, 

 and at all events it is surely not found in the cold depth of the Norwegian Sea. 



The species Ech. Alexandri and affinis, no doubt, are closely allied. As they are most fre- 

 quently found together, it is an obvious thought that they might possibly be one species with a 

 marked difference of sex, although such a difference is otherwise very unusual in the Echinids. Of 

 this, however, there can be no question, as I have found both $ and $ among specimens of affinis. 

 There can be no doubt that they are two well distinguished species. The form of the test, the 

 tubercles on the ambulacral areas, and especially the tridentate pedicellarise yield excellent criterions 

 of them. But on the other hand it may be very difficult or quite impossible to distinguish quite 

 young individuals of the two species, the more important specific characters being not yet typically 

 developed. From the Ingolf we have thus a rather great number of small specimens, which I am 

 not able with certainty to refer to one or the other of the two species. They are badly preserved, so 

 that no tridentate pedicellarise are to be found. These pedicellarise are otherwise early developed, and 

 give then all desirable certainty in the determination. The tridentate pedicellarise seem not rarely to 

 be quite wanting in larger individuals, as may also be the case in Ech. Alexandri; the determination 

 of such specimens will, however, scarcely cause any difficulty, as especially the arrangement of the 

 tubercles in the ambulacral areas then will be a sufficient criterion. 



15. Echinus acutus Lamk. 



PI. I. Figs. 4, 78. PI. II. Figs. 1 2, 6, 8. PL XV. Figs. 2, 1416. PL XVI. Figs. 2, 5, 10, 16, 18, 22. PI. XVIII. Figs, i, 57, 14, 24. 



PL XIX. Figs. 32, 36. PL XXI. Figs. 2526. 



Principal synonyms: Echinus Flcmingii Forb. 



norvegicus Dub. Kor. 

 depressus G. O. Sars. 



