Bull. U. S. B. F., 1923-24. (Doc. 963.) 
Fig. 13. — Frontal section of posterior ends of palps of L. luteola 10 mm. long, showing grooves on sides of ridges 
and posterior end of inner palp curled about, causing the grooves on the apposing face to be widened. A, foot; 
B, gill; Cand D, palps. X200. 
Fig. 14.— Cross section of ridges on inner face o' palp of adult L. luteola, showing grooves on (Ant.) anterior and 
(Post.) posterior sides. X100. 
Fig. 15. — Cross section of ridges on inner face of adult Quadrula pustulosa, showing a, posterior groove, and c, 
anterior groove. The evidence seemed to show that in the area abc the cilia beat toward Ant., while in the 
area cda they beat down the groove between the ridges. X100. 
Fig. 16.— The same as Figure 15, except that the background of the negative was painted out before the print was 
made. 
