MUSEUM OF COMPARATIVE ZOOLOGY. 197 



were collected by G. W. Webster at Hawk's Park, "widely distributed in dry 

 places, where other species are not found." Also at Hidalgo, Texas (Singley). 



The shell is figured on preceding page. 



The jaw (Plate III. Fig. 6) is high, strongly arched, with acuminated ends ; 

 it is very thin, membranous, light horn-colored and transparent ; there are 

 numerous some fifteen on each side the median line narrow, delicate ribs, 

 running obliquely to this line, denticulating either margin ; on the upper 

 median portion the ribs meet before reaching the lower margin, leaving upper, 

 median, triangular plates as in Orthalicus. The jaw is quite such as I have 

 described and figured for Macroceramus in Terr. Moll., V. 384. It also resem- 

 bles that of Microphysa turbiniformis (Ann. N. Y. Acad. Sci., III., Plate XV. 

 Fig. C), excepting that the latter wants the upper median triangular plates. 

 A greatly magnified view of the central portion of the jaw is given. 



The lingual membrane is long and narrow. Owing to its small size, it was 

 very difficult to determine the shape of any but the lateral teeth. Three of 

 these last are figured on Plate II., Fig. 5, drawn by camera lucida. They have 

 wide, square bases of attachment, bearing, as usual, two cusps, both stout and 

 blunt, aud bearing short, stout cutting points ; the centrals appear of the same 

 shape and tricuspid, but I failed to distinguish them clearly enough to draw 

 by camera ; the laterals are separated, low, wide, quadrate, with long irregu- 

 larly serrated cusp. I failed also to distinguish these clearly enough to draw 

 by camera. I have represented them in the figure as they appeared to me. 

 The laterals seern like the teeth of Pupa, the marginals much like those of 

 Cionella subcylindrica. The dentition is somewhat similar to what I have fig- 

 ured of vortex on page 356 of the Manual of American Land Shells. There 

 are about 15-1-15 teeth, with six perfect laterals on each side the median line. 



Mr. Dall says of this species that the shell is much smaller than that of 

 granum, olive-greenish, with a silky lustre and few inflated whorls, the first 

 of which is usually finely punctate. The suture is very deep, and the umbili- 

 cus is proportionally larger than in granum. 



The figure of the dentition of an undetermined species found by Dr. W. M. 

 Gabb, in Costa Rica, published by me in the Annals of the New York Acad- 

 emy of Science, Vol. III. p. 261, Plate XL Fig. G, is said by Mr. Pilsbry to 

 represent that of this species, he having identified the shell from which the 

 lingual was extracted to be H. cceca, Guppy. 



Hemitrochus varians, MENKE. 

 Strobila Hubbardi, BUOWN. 



Polygyra auriculata, SAT. 



Dall (U. S. Nat. Mus. Proc., 1855, p. 263) thus characterizes a variety 

 microforis : 



This form is quite well marked, and when fully adult shows as a rule little vari- 

 ation from tin- form tiiiun d |y the Binncvs, and iji'iierally regarded as typical. A 

 quite uniformly characterized variety was found, however, by me at Johnson 1 - 



