78 THE NiL.UTILUS. 



than 6 mm. A. parcdhlus is one of the few species o'i Ferrissia that 

 by preference chooses the quiet w,aters of the inhind lakes for its 

 home. In northern Michigan,, where it is ti;e only spepies found, it 

 is abundant on the under surface of the lily pads and on the round 

 reeds {Scirpu^ lacustris), gvowmg in water 3 to 6 feet deep. 



The dimensions of the specimens figured are as follows : 



Fig. 1. Length 6.5, breadth 3.10, alt. 1.76 mm. 



Fig. 4. Length 4.80, breadth ,3.25, alt. 1.75 mm. 



Fig. 7. Length 8.66, breadth 5.00, alt. 2.50 mm. 



V. Aacylus haldemani Bgt. (1844): PI. 6, figs. 9-13. 



Haldeman's types of the species, for which he used the preoccu- 

 pied name, of depressus, came from the headwaters of the Holston 

 River, in Washington County, Virginia, and are now in the collec- 

 tion of the Philadelphia Academy. Dr, Pilsbry has kindly fur- 

 nished the accompanying outlines of the larger of the two specimens 

 (figs. 9, 10), and states that " the base is a little raised at the ends, 

 but very slightly so, so that the growth-lines appear nearly straight. 

 There are some coarse radii, especially on the long slope, but not 

 noticeable over the whole surface, but the apical tract is beautifully 

 striate." 



I have referred to this species a small series collected by Hemp- 

 hill in the Doe River at Roan Mountain Station, Tenn. As shown 

 by the figures (figs. 11-13), they agree quite exactly with the type. 

 The specimen figured is decidedly obovate in its marginal outline, 

 the greatest width being behind the apex, but others are more regu- 

 larly oval. 



It is a well-marked form, and, as stated by Haldeman, differs 

 from both rivularis and tardus in the obtusely rounded apex, which 

 in the Doe River specimens is directed nearly straight backwards. 

 In the type specimen, it is apparently more excentric. There is no 

 indication in the Doe River specimens of the "coarse radii " which 

 are present on the type, but merely a slight rippling of the anterior 

 slope. But this, no doubt, is a variable feature. The specimen 

 figured is slightly longer and proportionately wider than the type ; 

 the dimensions being : Length 4.43, breadth 3.33, alt. 1.5 mm. 



VI. Ancyhs elatior Amh. (\S5o). PI. 5, figs. 10-12. 



Through the kindness of Mr. L. P. Gratacap of the American 



