THE NAUTILUS. 29 



Thirteen species were obtained, and may be noted as follows: 



1. 'CIRCINARIA CONCAVA Say. A number of large and typical 

 specimens of this species were collected and kept alive for a long 

 time on the writer's desk. On May 18th two individuals were noted 

 in coitu, the coitus lasting from 8 o'clock A. M. to 6 o'clock P. M. 

 During this time both animals were perfectly quiet, the eye pedun- 

 cles and tentacles drawn into the head and the foot contracted to 

 form a rounded oval. During the coitus the heart, which normally 

 beats about 75 times per minute, was reduced to 19 very slow and 

 long beats. The foot of the snail taking the active part was partly 

 covered by the passive snail, and the former's head was slightly 

 lifted. The specimens measured about 15 mill, in greatest diameter. 



2. VITREA ARBOREA Say. A few specimens of this species were 

 obtained under and in rotting logs. All were perfectly typical. 



3. OMPHALINA FULIGINOSA Griffith. The specimens obtained 

 were rather dark in color and about half grown, the umbilicus wide 

 and deep. 



4. POLYGYRA (MESODON) ALBOLABRIS Say. But a single speci- 

 men of this species was obtained alive, and that was very large, 

 measuring 34 mill, in greatest diameter. The animal was kept in 

 captivity for several weeks, and was more active than any of the 

 other species of Mesodon that the writer has studied. It wasstarted 

 at the bottom of a book case door four feet long and reached the top 

 in about half an hour. The examination of the lingual membrane 

 gave 45-1-44 teeth with ten perfect laterals. In this membrane the 

 38th tooth was abnormal in having three well formed cusps of equal 

 size, instead of a bifid inner cusp. 



5. POLYGYRA (MESODON) EXOLETA Binney. Several typical 

 specimens of this species were collected, among which there was one 

 without the parietal tooth. The lingual membrane of one specimen 

 gave 47-1-47 teeth with eight perfect laterals. The marginals 

 were very variable, some being with and some without side cusps. 

 It is probable that several teeth were torn away from this mem- 

 brane, although there could not have been the normal number given 

 by Binney, 60-1-60. 



6. POLYGYRA (MESODON) THYROIDES Say. All specimens were 

 of the normal form. 



J For the change in names of several of the genera and species here listed, 

 see Pilsbry, Proc. Phila. Acad., 1894--97, where adequate reasons are given. 



