ECHINOIDEA. II. 



P. hirsutus and Nordenskjoldi have the labrum in contact with the sternum, this feature tnns evidently 

 pointing towards the Urechinids. It thus seems evident that Plexechinus must be referred to the 

 Urechinida ; but it must be conceded that the position of the anal system and especially (what Agas- 

 siz seems to have overlooked) the shortened anterior ambulacrum show it to be a somewhat modified 

 type; it is also worth noticing that there is a faint trace of a deepening of the anterior ambulacrum 

 (more distinct even in P. Nordenskjoldi}. These characters point towards the Pourtalesise and may 

 perhaps indicate that the latter have developed from forms like Plexechinus, though the different 

 structure of the paired anterior interambulacra evidently forbid thinking of a direct derivation of the 

 Pourtalesise from the Urechinidce ; the structure of the test of the Pourtalesia; is more in accordance 

 with the Echinocorythince , and it would, indeed, seem more natural to suggest that the Urcchinidce 

 and the Pourtalesiida are two separate branches from the Echinocorythidtz (Ananchytidce). - The 

 resemblances between Plexechinus and the amphisternous Palceotropus pointed out by Agassi z can 

 scarcely be more than superficial analogies. Upon the whole I do not see the reasons why the typical 

 amphisternous Palceopneustida' should be reckoned among the sAnanchytid Spatangoids, as is done 

 by Agassiz (Panamic Deep-Sea Ech. p. 150). 



Fam. Pourtalesiidae. 



21. Pourtalesia Jeffreys! Wyv. Thomson. 



PI. V. Figs. 1314, 16-19, 2'. 2 3- PI- VII. Figs. 2 4, 1112, 14, 21. PI, VIII. Figs. 4-6, 8- n. PI. XI. Figs. 4, 7 10, 30. 



Wyv. Thomson: Depths of the Sea. p. 1089. Fig. 12. p. 457. (394) Ann. Nat. Hist 4. Ser. X 

 p. 305. Porcupine >-Echinoidea. p. 747. PL LXX. i 10. PL LXXI. -- Loven: On Pourtalesia. PL I V 

 PL XII. 149. -- Danielssen: Echinida. Norske Nordhavs-Expedition. p. 5. -- Pfeffer: (319) p. 101. - 

 Agassiz: Echinoidea. (Knight Errant) (10). 0stergren: (450) p. 253. -- Hoyle: Rev. List British 

 Echinoids. p. 430. -- Koehler: (233. b). -- Doderlein: Arktische Seeigel. Fauna Arctica. p. 385. Echi- 

 noiden d. deutschen Tiefsee-Expedition. p. 268. Grieg: Echinodermen v. d. norwegischen Fischerei- 

 dampfer Michael Sars^ in den Jahren 19001903 gesammelt. I. Ophiuroidea. p. 14. Bergens Mus. Ar- 

 bog. (1903). -- Michailovskij: Zoolog. Ergebnisse d. Russischen Exped. nach Spitsbergen. Echino- 

 dermen. Ann. Mus. St Petersbourg. VII. 1902. p. 524. Nachtrag. Ibid. VIII. 1903. p. 393. Die Echino- 

 dermen der zoologischen Ausbeute des Eisbrechers Jermak* vom Sommer 1901. Ibid. IX. 1904. p. 163, 

 184. -- Knipowitsch: Explorations zoologiques sur le bateau casse-glace <Ermak en ete de 1901. 

 Ibid. VI. 1901. p. IX, XV. -- Kolthoff: Til Spetsbergen och Nordostra Gronland Ar 1900. p. 176, 210. 



Non.: Rathbun: Catalogue of the Echini of the U. S. Nat. Museum. (337) p. 287. -- Verrill: 

 Results of the Explorations of the Albatross* 1883 (4 2 6)- P- 539- Norman: Notes on the French 

 exploring Voyage of <Le Travailleur in the Bay of Biscay (302). p. 435. 



The rich and partly well preserved material of this species collected by the -Ingolf^ enables me 

 to give a little additional information thereof, though, of course, not much remains to be done after 

 the elaborate descriptions given by Wyv. Thomson and especially by Loven in his classical work 

 On Pourtalesia.). The most needed information, viz. that of the development of the test from quite 



