130 MAIUNR ANIMALS. 



localities before named, and I found this morning, (April 2nd., 18o3,) two 

 specimens at the roots of decaying herbage on the rocks of the Hoe. 



Clausilia nigrican.s, Linn. — Very common: various habitats in various localities; 

 I find it more frequently at the basement of walls. 



Carychium minimum. Leach. — Rare: one specimen on a piece of decayed 

 wood in Manodon Wood, 



Acme fusca, Grm/. — One dead specimen found in moss. 



Limncus pereger, Drap. — In ditches and stagnant pools: very common. 



Limneus palustris, Drap. — Not common: in stagnant water near Millbrook. 



liimneus truncatulus, Linn. — Very common in ditches, frequently in company 

 with L. pereger. 



Ancylus fluviatilis, Midler. — In streams and on the rocky beds of rivers. 



Physa fontinalis, Drap. — In a stream of water near Radford. 



Planorbis laevis. Gray. — In a stream or drain in the grounds of Mr. Cornish. 



Planorbis vortex. Mailer. — In a ditch near the embankment. 



Cyclas cornea. Lam. — In a pond near the new road. 



Cyclas lacustris, Turton. — In company with the above. 



Pisidium pusillum, Grat/. — In a small pond near Weston Hills, one specimen. 



Alasraodon margaritiferus, Gray. — Specimens from the Plym. 



A_pril 4:th. 1853. 



MARINP] ANIMALS. 



MOLLUSCA.— Part III. 



BY O. S, ROUND, KSQ. 

 ( Continued from jjaffe 92.^ 



I PROMisRD in my last paper to proceed at once to consider the interior 

 structure of the "Conchifera," which may be said to be a recent addition to 

 the Molluscous animals, but I find so much of interesting matter still connected 

 with the shells, that my readers must pardon nie if I keep them on the 

 outside a little longer. It will be remembered that I spoke of the structure 

 of all this tribe, and especially the "Pinna" or common Oyster, as cellular, 

 or not solid, but composed of a series of cells or vacant spaces, which in 

 common parlance would be called "tubes," (see Fig. 5.) For so thin a thing as 



a shell this may at first seem startling, 

 but when we are a little acquainted 

 with microscopic proportions our wonder 

 will cease, that there should be such 

 things, and begin, when we know that 

 they exist. Now, "Exceptio probat regu- 

 lum,^' and so although, as a general 

 Fm. 3. -Section of the Pinna Shell, Tube. r\x\Q, these shells are cellular and tuberous, 



shewing the direction of the Cellular •' ' 



Tubes. it is only the perfect layers that are so, 



