44 



RANELLA. 



except by one with very sharp eyes. They occur on 

 the southern coasts. 



From these very small shells we pass abruptly to a 

 very large one, Ranclla Californica^ Hds., Ra-nel'-la 

 Cal-i-for'-ni-ca, commonly known as the Frog Shell. 

 The picture of a small specimen is shown in Fig. 24. 



This shell is ver}' strong and 

 solid, and its surface is marked 

 with many knobs and ridges. It 

 appears to grow forward half a 

 whorl, and then the creature 

 pauses and builds up a thick lip. 

 Leaving this ridge at length, it 

 completes the whorl, and then 

 forms another varix. The result 

 of this singular method of shell- 

 building is, that the shell has 

 two ridges extending from the 

 apex to the canal, on opposite 

 sides of the whorl. This feature 

 is characteristic of the whole Raiiella genus. 



Our species is essentially a southern mollusk, though 

 I have seen a few good specimens which were collected 

 in Monterey Bay. 



The external color is yellowish brown ; but within 

 it is of the purest white. The common length of 

 one of these shells is three inches, though some of 

 them grow to twice that length, and thus rank as one 

 of our largest shells. 



At this point, mention should be made of the rare 

 Prune Oregoneiisis^ Redf., which has a large, elon- 

 gated, thin shell, with distinct, rounded whorls and 

 a short canal. It is of a light color, and is covered 

 with a hairy epidermis. Its home, as the name indi- 

 cates, is on the northern coast. 



