316 WEST COAST SHELLS 



Lea, Nuttall's Flood-shell. It is a more 

 slender species than either ot the pre- 

 ceding; yellow-brown or dark colored. 

 Habitat similar; found in the Columbia 

 System. 



Fig. 299 



THE VALVE SHELLS 



{Valvatidi^) 



This group contains the single genus Valvata. 

 They have small, umbilicate shells with rounded or 

 angular whorls of a green, pellucid, or brown color 

 and live in lakes and ponds. 



Valvata virens^ Tryon, the Green Val- 

 vata,^ Figure 300, is a species found in the 

 Coast Range System. It is light to dark 

 green with a fairly high spire and a deep 



u U-1- -ru U 1 Fig. 300. xi 



rather narrow umbilicus. 1 he whorls are 

 rounded and smooth. 



Valvata Jiumeralis, Say, the Western Valvata, 

 PL II, Fig. 6, is blue-green or brown. It is smooth, 

 somewhat flattened beneath, has a broad umbilicus 

 and a flat-topped somewhat elevated spire. Found 

 all over the West Coast and in Mexico. According 

 to Dr. Pilsbry the torm on the Paciiic Coast south 

 to Sonora should be known as Valvata humeral is 

 calif ornica^ Pils. 



THE VIVIPAROUS SHELLS 



(^Viviparida:) 



This group of large shells is not native on the 

 Pacific Slo[)e, but is found in the Eastern States 

 and Eurasia, and one species has been introduced. 



