AND ALLTKD FORMS, 15 



two outer ones large. The upper margin of the rhachidiun tooth 

 is concave, and its broad cusp' is 7 -denticulated — the central 

 denticle being large (larger than i.s represented in the cut), though 

 but little projecting, while the three lateral ones on each ;?ide are 

 small and equal. The intermediate tooth (" zwischenplatte") is 

 very considerably produced and narrowed below, so that its body 

 is very small and its peduncle long, and the body has a strongly 

 projecting knob at its infero-interior angle. Its cusp is armed 

 with five strong, sub-equal denticles — the inner one being rounded 

 and blunt, while all the rest are acutely triangular and strongly 

 projecting. There seems to be also a minute denticle on the 

 inner side of the large inner denticle. The two lateral teeth are 

 long, slender, and curved ; the terminal margin of the pointed 

 inner one being armed with about eighteen minute denticles, and 

 the rounded extremity of the outer one being so minutely serrated 

 that the denticles, thirty or forty in number, can only be perceived 



under very high powers of the microscope 



Of the Amnicola porata the males and females occur in about 



equal numbers. The ova are deposited, in this latitude, during 



the months of April and May. The ova-capsule (Fig. 7) is thin, 



corneous, of a semi-lenticular shape, and 



attached by the cut face of the lens, which 'S' 



forms the base. The free limb is margined 



with a broad thin lamina of the same delicate 



horny texture as the envelope of the capsule 



itself. In size, these ova-capsules are a little 



larger than the head of the animal. They 



are* deposited singly, and each contains but 



a single egg, which floats freely about in the 



fluid surrounding it. Those which occurred to me were found 



sticking to the shell of a female, although they were proI)ably 



not deposited by the same individual, but by some other, while 



they were huddled together in groups according to their practice 



at this season. 



It will be noticed that this description of the ova-capsule does 



I It must be remarked that in the view of the teeth which is usually 

 presented under the microscope, and which is represented in every dia- 

 gram of a single row, the denticles of the cusps of the teeth appear fore- 

 shortened, and thus much shorter and blunter than they really are. 



