Revision of the. genus Behmnocrinus, etc. 253 



left visual line, by the law stated above, are brought together 

 and superposed. 



One thing more to complete the explanation. The impres- 

 sion on ther'mii: rw [...-vail-over that of the left— the impression 

 of the circular area obliterate* that of the corresponding spot 

 on the hand or paper sheet, for two reasons ; first, because the 

 circular are; . ated from the rest of the right 



eye field of view (the dark interior of the tube) while the cor- 

 responding spot on the left-eye field is not thus differentiated ; 

 and second, because both eyes are focally adjusted for the dis- 

 tance of the object seen by "the right eye only. Thus it comes 

 to pass, that the right eye sees only -'-' 1- est of its 



field being very dark : while the left eye sees all its field 

 except the' spot covered 1 \ the circular area. Cut if an ink 

 spot be placed on the hand or paper sheet just where the 

 visual line pierces, then the first cause mentioned above will be 

 removed and the strongly differentiated ink spot will be seen 



Berkeley, Cal., Feb. 7, 1877. 



Art. XXVIIL—Bevi on of the genu Belemnocrinus, and de- 

 scription of two n?w species; by Charles Wachsmuth and 

 Frank Springer. 



In 1862, Dr. C. A. White described a type of Crinoids from 

 the Burlington limestone of Iowa under the generic name Be- 



!<-< -rinus, ot which he had discovered or. 



£ typm. The description, with a figure, was published in the 

 tv of Natural History, vol. ix, p. 

 13. Messrs. Meek an. : 1 *> rt of f he Geological 



Sun . . I ,. ,. . . iii. p 463, described another species, B 

 - ."■'■■'," 



parative Zoology at Harvard College, No. 8, p. 29 has made 

 some interesting observations u P 



to the recent genus /; ; the opin- 



ion that BelJinocrin* ^PP os f, d ' 



five small ^wl? 



- ,-xhibiting : 



ark,-d 



A careful examination of some recently acquired specmens 



'" <«-emis ineludiu" two now species man excellent state 



