MAZATLAN BIVALVES 19 



perhaps from living near the outside, and therefore being 

 easily washed out ; L'pool fy Havre Coll* 



Tablet 65, 4 young valves. 66, 2 pairs, 2 valves, adolescent. 

 67, 2 pairs, adult. 68, 2 pairs bored into and distorted. 69, 

 specimens of dried foot. A burrow may be seen in ?36, and a 

 specimen in situ among the Chamse. 



25. PETRICOLA VENTRICOSA, DesJi. 



Proc. Zool. Soc. 1853, ?ubi. B. M. Cat. Yen. p. 214, no. 22. 

 = (teste Sow.) P. denticulata, Sow. Proc. Zool. Soc., 1834, p. 46. 



Sow. Thes. Condi, part xv. p. 773, pi. clxvi. f. 6, 7. B. M. 



Cat. D'Orb. Moll. p. 64, no. 564 B. M. Cat. Yen., p. 213. 



no. 21. 



This shell agrees with the description of P. ventricosa better 

 than with that of P. denticulata, and must rank with that species 

 if they prove distinct. If they are identical, as Sow. supposes, 

 his name, though not so expressive, has priority. It takes 

 both the elongated and abbreviated forms. Long. '26, lat. '36, 

 alt. '23. 



Hab. (P. denticulata) Payta (Peru) in hard clay and stones at 

 low water, Cuming. Arica, D'Orbigny. (Var. abbreviata) 

 Isle Plata, Cwming. Payta D'Orbigny. (P. ventricosa) 

 Gulf of California, Mus. Cuming. Mazatlan : burrowing in 

 Strombus galea, extremely rare, Havre Col. Received with 

 other shells from the West Indies, P. P. C. 

 Tablet 70 contains 2 opposite valves. 



26. PETRICOLA , sp. ind. 



Tablet 71 contains a rugose fragment, apparently not identi- 

 cal with any published species from the W. American coast. 

 Hab. Mazatlan : in Spondylus Lamarckii : L'pool Col. 



* I strongly suspect that this species is also found on the W. African coast. I 

 have a valve, received from the Bristol Institution where it had been before they 

 had a single shell from the West Coast of America that I know of, and before 

 Cuming's discoveries there. At that time there was plenty of trade between 

 Bristol and Africa ; and I believe the species came out of Ostrea iridescens of 

 which they had a large stock. Vide remarks on [that sp. and Placunanomia. If 

 P. typica, Sow. Thes. Conch. No. 13. does not differ from robusta more than is 

 there stated, it is probably the same species, from St. Thomas, W. Indies. 



