Bd. VI: 4) THE ECHINOIDEA. 59 



In 1 88 1 Prof. Bell described, in his Report on the Echinoderms collected by 

 the »Alert» in the straits of Magellan and on the coast of Patagonia (Proc. Zool. 

 Soc. London 1881, p. 88), a new species of Strongylocentrotus, named Str. bullatus. 

 In discussing its relation to the other species of the genus Bell points out that >it 

 seems to be the only species in which all the ocular plates are excluded from the 

 anal system — presenting a considerable resemblance to S. franciscanus, in so far 

 that the primary tubercles of the interambulacral area; form, in both species, two 



rows, and are considerably larger than any others on the test So, again, 



a resemblance is to be seen to S. albus in the presence of the tubercles separating 

 the arcs of pores; but these tubercles are much smaller and much more irregular in 

 5. bullatus, and this new species has also a somewhat larger mouth (actinostome)*. 



In spite of the differences here pointed out I must regard bullatus as a synonym 

 only of albus. Regarding the ocular plates there is, as has been shown above (p. 54), 

 so considerable a variation that no reliable specific difference can be found in the re- 

 lation of these plates to the periproct. The size of the tubercles separating the arcs 

 of pores is likewise too variable to be relied upon, and likewise I cannot agree that 

 they are more irregularly arranged in »bullatus» than in albus. Finally the size of 

 the actinostome! On p. 425 — 26 of his paper Observations on the characters of 

 the Echinoidea IV. The Echinometridae» (Proc. Zool. Soc. 1 881) BELL gives some 

 measurements of specimens of both species, one of each being 115 mm. in diameter; 

 the percentage value of the actinostome for these two specimens is given as 20.9 in 

 albus, 23.04 in bullatus; in the other specimens the percentage value of of the actino- 

 stome is calculated to 21.9, 24 and 27.4 for albus, 30.8, 31.6 for bullatus. For the 

 specimens of which the measurements are given above (p. 53) the percentage value 

 of the actinostome becomes: 25.05, 28.35, 30-42 and 22.13. This shows that the size 

 of the actinostome is also too variable for being used as distinguishing character. 

 The specimens measured here show the same range of variation in regard to this 

 character as both the »species» of BELL — and that these specimens are really all the 

 same species, can in no way be doubted. The distinguishing characters pointed 

 out by BELL between albus and his species bullatus are thus irrelevant, and I am 

 unable to find any better ones. Also the pedicellarias are alike, as I have stated in 

 the »Ingolf» Echinoidea I. (p. 123). (Regarding the small form of tridentate pedi- 

 cellaria; described from »Str. gibbosus* (= L. albus) in this place, cf. above p. 55.) 

 The colour of the test of bullatus, it is true, is described by Bell as »brownish red», 

 which is not in accordance with the characteristic colouration of albus described above 

 (p. 55). The reason of this difference, however, is no doubt to be found in the 

 fact that Bell's specimens have been dried without having the skin cleaned off, 

 which is rather thick and brownish pigmented. — The result is that Bell's Stroti- 

 gylocentrotus bullatus must be regarded as a synonym only of Loxechinus albus; 



