138 ROBERT TRACY JACKSON ON ECHINI. 



tant, I collected the 7,600 specimens here described. At this locality individuals do not attain 

 a very large size, and observations were on various sizes without measurements, though none 

 was very young. Of arrested variants, 3.2 % have ocular I only and 0.07 % have V only insert; 

 94 % have I, V; 1.6 % have I, V, IV; and 0.03 % have I, V, IV, II insert, thus presenting a wide 

 range of characters. Aberrant variants are of many characters as might reasonably be expected 

 in a large series, yet are relatively not numerous, only 76 specimens, or 1 %. Of these, one 

 specimen has ocular IV only insert (text-fig. 140), a very rare variant in Echini; six specimens 

 have oculars I, II insert; seventeen I, IV; nine V, IV; and eight V, II insert. Thirty-two 

 specimens have oculars I, V, II, and two have V, IV, II insert, the latter a very rare variant 

 (text-fig. 148). One specimen has oculars I, V, IV, III insert, II exsert. This very rare variant 

 was seen in only one other specimen of this species (text-fig. 149, p. 134). The character of the 

 Echini as regards ocular plates from the Calderwood locality is practically the same as in the 

 Dumpling Island specimens, but is slightly more progressive. 



At York, Maine, a series was collected in tide pools. The conditions are rocky shores 

 exposed to the open ocean. The specimens (2,700) varied in size from small to large, but none 

 was very young. Only 0.9 % have ocular I alone insert, a smaller proportion than in any 

 locality previously considered. Oculars I, V are insert in 97 %, the highest average of any 

 locality studied. As this is the species character, specimens from this locality may in a sense 

 be considered as the nearest approach to the ideal of the species. As progressive variants, 

 1.4 % have oculars I, V, IV insert and one specimen (text-fig. 139, p. 132) has oculars I, V, IV, II 

 insert. The aberrants are relatively few, 0.9 %. They are two specimens with oculars I, IV 

 insert; six with V, IV; six with V, II; and eleven with I, V, II insert. It is interesting to see 

 that in these later series, as the relative frequency of oculars I, V, IV insert increases, con- 

 currently the number of the aberrant variant I, V, II insert proportionately decreases. 



Up to this point the series from the several localities have gradually decreased in the prim- 

 itive character of ocular I only insert and gained in the species character, the bivium insert, 

 finding its maximum of 97 % in the York locality. There has also been a slight gain gradually 

 in the progressive character of oculars I, V, IV insert. From here on in the succeeding locali- 

 ties considered, with slight fluctuations, the bivium gradually decreases its dominance and the 

 progressive variants concurrently increase, thus approaching other species of the genus which 

 are further evolved in this character (compare pp. 143 and 162). 



Mr. A. P. Romine very kindly sent me a fine series of this species from Friday Harbor, 

 Puget Sound, Washington. The locality is at the entrance to the Sound, and the water is 

 presumably typically salt. The specimens average large, those tabulated ranging from 40 to 85 

 mm. in diameter. A specimen of S. drobachiensis from Alaska, in the United States Fish 

 Commission Collection, measures 90 mm. in diameter, but otherwise the maximum Puget 

 Sound specimens are the largest seen or recorded. Of this series, in 1,200 specimens, 96% 



