310 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 8 



Family ScutcllidaC 

 Dendraster excentricus Eschscholtz 



Plate 49, Fig. 32 



Scutella excentrica Eschscholtz, 1831, p. 19. 



Dendraster excentricus L. Agassiz and Desor, 1847, p. 135. 



Echinarachnius excentricus A. Agassiz, 1873, pi. 13a, figs. 1-4. 



There are literally thousands of specimens of this common and char- 

 acteristic west coast sand-dollar in the Velero collection but as rather 

 more than eleven thousand are young individuals less than 10 mm in 

 diameter they offer no help in the almost hopeless attempt to distinguish 

 reliable specific and varietal lines in the mass of material at hand. Leaving 

 obviously very youthful specimens out of account, there are approximately 

 750 specimens to vi^hich it should be possible to attach varietal if not 

 specific names, for the alternative of calling them all excentricus is simply 

 an evasion of the problem. After long and critical study of all the usable 

 specimens which are past 30 mm in diameter, and of scores of smaller 

 specimens as well, it seems necessaiy to recognize 3 species and one named 

 variety in addition to the long known excentricus. It should be added at 

 once that this does not leave excentricus a constantly well-defined species. 

 Far from it! In the material here identified as excentricus sens. str. there 

 are many specimens which differ obviously from a typical individual, 

 though they come from the same region and even from the same station. 

 In the absence of still more abundant material, the only practicable course 

 is to list them as excentricus, pointing out the features in which they are 

 puzzling. 



Normal specimens may reach a very large size, the largest coming 

 from the northern stations. Specimens from the Oregon coast are fre- 

 quently 75 mm long, 80 mm wide and 12-14 mm high (or thick) ; the 

 largest in the Velero collection is 87 mm long and 95 mm wide. Ordinary 

 specimens from Monterey and southward are usually less than this, a 

 t>-pical specimen being 65 x 70 x 9 mm but there is a great deal of diversity 

 in shape and stoutness. Among the Channel Islands and south to Corona 

 del Mar, this sand-dollar is very common in shallow water, from low 

 water mark down to at least 40 fms. South of the Mexican line there 

 seems to be a tendency to a more elongate form and a variety elongatus 

 was described in 1935 (H. L. Clark, p. 122). The present collection con- 

 tains few specimens that can be referred to this variety and 8 of these are 

 young bare tests (bleached), 7 from the vicinity of Cedros Island, Lower 

 California and 1 from ofl San Nicolas Island, California. A fifth speci- 

 men is very different in appearance from these tests for although it is also 



