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Cincinnati Society of Natural History. 



Unio lachrymosus Lea. Heart very active and regular ; 

 pulsations 31 to 33 per minute. 



Unio pustulosis Lea. Pulsations regular, 23 per minute. 



Unio ventricosus Barnes. Pulsations regular, 17 to 18 per 

 minute. 



Unio parvus Barnes. Pulsations regular, 36 per minute. 

 This is the largest number recorded for the genus Unio. 



Unio spatulatus Lea. Pulsations regular, 16 per minute. 



Sphcsrium stamineum Conrad. Pulsations regular, 57 per 

 minute. This number is unusually high for a pelecypod, but 

 the animal is very active, which accounts for the high rate of 

 pulse. 



Selenites co?icavus Say. The heart is situated 5 mm. from 

 the edge of the aperture, and is plainly seen through the trans- 

 parent shell, especially if it be moistened. The pulsations 

 are very regular, but vary in number, being more numerous 

 when the animal is stretched out as during locomotion, and 

 few when the animal is contracted. From twenty observations 

 the following data are taken, ranging from the lowest to the 

 highest number : 50, 56, 72, 75, 78, 82. Temperature affects 

 the heart's action, cold causing it to cease beating apparently, 

 and heat causing it to beat very rapidly ; 50 is the normal 

 when contracted and 82 when extended and active. 



Vitrea arborea Say. Pulsations rapid and regular, varying 

 from 100 (contracted) to 160 (expanded) per minute. 



Vitrea nitida Miiller. Pulsations varying from 101 to 138. 



Vitrea cellaria Miiller. The pulsations are regular when 

 the animal is extended, but seem to be irregular and inter- 

 rupted when the animal is contracted. The pulse varies from 

 46 to 84. When contracted the beats may be represented by 

 the following diagram, in which the dot represents the period 

 of rest between the beats, and the dash the length of the beat : 



Vitrea electrina Gould. Pulsations regular, varying from 

 95, when contracted, to 130 when extended. 



Vitrea indentata Say. The pulsations in this species seem 

 to be always high, the writer being able to record only 160 to 

 162 beats per minute. 



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