1 882.] Zoology, 9C9 



recently described 1 the efferent ducts of the salivary glands 

 which issue at the bases of the grooves of the teeth, evi- 

 dently with the effect to earn' the saliva into the wound. I ob- 

 served this many years ago, but do not know whether I published 

 it, and I gave the Arizona species the name of suspectum on ac- 

 count of the impression I derived from the observation of this 

 fact. It is, however, true that even small animals do not always 

 die from the effect of the bite. Perhaps the condition of Helo- 

 derma in this respect is like that of the Opisthoglyph serpents 

 which have a similar arrangement of one or more of the poste- 

 rior maxillary teeth, and are harmless to man at least.— E. D. Cope. 



A LAND SHELL NEW TO THE UNITED STKTm.—Ampelita rOWeM 



Newcomb can now be added to the .fauna of the United States. 

 The habitat of this specie.-, is given as Lower California in Binney 

 and Bland, Part 1, and " has been accredited to Arizona, but not 

 on undoubted authority" (see note 256, Binney's later work). 



I now have specimens collected on the Salt River mountains, 

 about seven miles south of Phoenix, Arizona, and determined 

 from the type for me by Dr. Newcomb.— Henry Prime. 



Gav arret on Astigmatism (Rc7 m Scuntifiqiu 1 J, Juillet, 1882). 

 —Astigmatism is an anomally of refraction of the eye caused by a 

 difference in the refringent powers of its meridian. This may be 

 caused by asymmetry of the curve of the cornea, (the most usual 

 case) or of the crystalline lens, or of both. The variation may be 

 regular or irregular. If a series of concentric black circles be 

 placed in front of an astigmatic eye, the circles will appear, if the 

 astigmatism be regular, as ellipses with their major axes in the 

 meridian of the eye having the greatest radius of curve, but if 

 the astigmatism be irregular, the margins of the circles will be 

 irregular. 



Regular astigmatism can be corrected by a suitable lens of 

 spherical section or a combination of cylinder and sphere. 1 he 

 power of accommodation possessed by the crystalline lens inter- 

 feres with a correct result. To obviate this atropine has been 

 used, but this, besides other evils, may also give incorrect results, 

 dependent upon the susceptibility of the patient. 



The ophthalmometer of Helmholtx is an ingenious instrument 

 for the measurement of this asymmetry, but the examination of 

 a single eye needs eight readings of the instrument and long 

 calculations. , . _ c . 



A far simpler ophthalmometer has been invented by Drs. Saval 

 and Schiotz. It depends upon the fact that, if the diseased eye 

 be looked at through a lens of 10 to 20 centimetres, focus, placed 

 in a small hole pierced in the centre of a square of white paste- 

 board, the image of the square, reflected by the eye examined, 

 will be rectangular in proportion to the degree of the astigmatism. 



1 Verhandlungen des vereins fur Natunvisseiii-cliafc, v, 1SS2, fol. HI. 



