464 



LAUOHTON 



[chap. 18 



Fig. 34. 118°38'\V, 32' 22.5'N. Depth 549 m. Inshore continental slope off southern 

 California. (U.S. Navy Electronics Laboratory photo by C. J. Shipek.) 



A green mud bottom highly disturbed by benthonic activity showing a mound 

 and depression of biological origin, plus numerous tracks formed by sea-urchins 

 (echinoids). 



Fig. 35. 38° 20'N, 28° Ol'W. Depth 1628 m. Mid-Atlantic Ridge near Pico, Azores. Area 

 of picture approx. 1 m by 70 cm. (Photo by L.G.O.) 



An example of one of many such (racks found on soft nuiddy bottoms being made 

 by a scapliopod-like animal with two long arms. The track shows a characteristic 

 angularity due to the area swept out when the rigid shell is pivoted. 



