MARINE MOLLUSKS — MACGINITIE 147 



Family Cryptochitonidae 



Genus Symmetrogephyrus Middendorff, 1847 

 Symmetrogephyrus vestitus (Broderip and Sowcrby, 1829) 



Plate 17, figures 1, 2 



Chiton vestitus Broderip and Sowerby, 1829, p. 368. — Sowerby, 1841, pi. 171, 



Chiton, fig. 128. 

 Amicula vestita J. Gray, 1847b, p. 69.— Oldroyd, 1927, pt. 3, p. 322. 

 Symmetrogephyrus vestitus Dall, 1921, p. 198. — Abbott, 1954, p. 316, fig. 66c. 



Forty-two specimens were dredged: 1 at 138 feet, 1 at 152 feet, 3 

 at 217 feet, 1 at 295 feet, 2 at 328 feet, 10 at 341 feet, 4 at 420 feet, 

 5 at 438 feet, 12 at 453 feet, 2 at 522 feet, and 1 (11 mm. long) at 

 741 feet. They range in length from 11 to 62 mm. 



On the epidermis of one chiton from 453 feet an amphipod was 

 cm-led up in a depression formed to fit it. Young barnacles may be 

 attached to the tips of the valves and foraminifers are often nestled 

 in the depressions formed at the junction of the plates and epidermis. 

 Around one plate there were 11 foraminifers of varying sizes. For- 

 aminifers may also nestle in the epidermis and form depressions to 

 fit, as they do on tunicates. On the chiton from 295 feet, over 15 

 foraminifers were thus embedded, some so deeply that, with their 

 covering of detritus, they were difficult to see. Also on this chiton, 

 growing attached to or near the base of some of the tufts, were small 

 colonies of the bryozoan Coriella siolonata. 



Other material examined: Over 20 specimens from locahties 

 ranging from off Cape Sabine in the Arctic to Kyska Harbor in the 

 Aleutians; 6 specimens from Nova Scotia, Maine, and Massachusetts 

 Bay. 



Discussion: In this chiton only the apex of the valve is visible, the 

 remainder being covered by the expanded girdle, which is dotted 

 with irregularly spaced tufts of stiff bristles. Relatively more of the 

 surface of the valves is visible in smaller than in larger specimens. 

 The gu'dle is cream colored, the bristles bro^vnish. 



The most noticeable variation is in the number of tufts of bristles. 

 In some specimens the tufts are very sparse, in others unusually 

 thick. Some of the specimens from Point Barrow are fairly thickly 

 tufted (pi. 17, fig. 1), others have very few tufts (pi. 17, fig. 2). In 

 4 specimens from Bering Island the tufts average only about 1 mm. 

 apart. The size of the tufts varies in any individual specimen as 

 weU as in different individuals. The spicules on the epidermis may 

 be sparse or thick. 



Distribution: Point Barrow south to the Pribilofs, Kyska Harbor 

 in the Aleutians, Hagemeister Island in Bristol Bay. Dall (1921) 

 gives the Atlantic range as "south to Cape Cod." It is new to Point 

 Barrow. 



