MAZATLAN BIVALVES 25 



young as much as in the adult shells. A very small specimen was 

 found to contain a minute young one. Specimens as broad as 

 '2 in. are very uncommon. One specimen was found having its 

 siphon pipe projecting nearly half the breadth beyond the shell. 



Smallest specimen measures long. '02, lot. '03 alt. '015. 



Elongated '03, 1, '02. 



Oval '2, '26, '14. 



Largest '18, '31, '14. 



Hob. Mazatlan : inhabiting the burrows of worms and Mol- 

 lusks in Chamse and Spondylus Lamarckii; also in dead Balani 

 on Strombus galea ; not uncommon ; L'pool fy Havre Coll. 



Tablet 80 contains 22 valves and 1 pair, jun. of various 

 shapes. 81, a pair of regular shape with young nullipore grow- 

 ing on ; pair with long siphon pipe ; valve with internal lamina ; 

 5 broken valves shewing hinge structure, &c. 82, the largest 

 specimen, from hole of Lithodomus caudigerus in Strombus 

 galea ; a Balanus with oval Sphsenia taken from within. 



We insert here a notice of a unique shell described by A. 

 Adams in the An. Nat. Hist. 1854, p. 418, under the name of 

 Tyleria fragilis. Though named in honour of Mr. Tyler, he had 

 it in his possession a considerable time without knowing of any 

 thing remarkable attending it. I have taken several journeys 

 to Liverpool and made enquiries in London, in hopes of seeing 

 it, without success ; but, as evidence that it is not mythical, I 

 deposit, on Tablet 83, drawings made by Mr. Sowerby and 

 most kindly placed at my disposal by H. Adams, Esq. It 

 is possible that it is a deformed shell. I have occasion- 

 ally noticed valves of Sph. fragilis with a tendency towards 

 the same crenation at the posterior end, apparently through 

 irritation of sand, &c. ; also with the pallial line broken up. 

 Mr. Tyler states that he found it in a burrow in the large 

 Spondylus from Mazatlan ; L'pool CoL 



Aug. 1855. 



