PREEACE. 



"The Collection, from wMcli tlie shells described in the 

 following pages have been carefully selected, was made at 

 Mazatlan, {lat. 23" N., long. 107° W.) dtiringthe years 184S-50, 

 by a Belgian gentleman named Frederick Eeigen." The bulli 

 of that portion of it quoted in the following pages as the 'Liver- 

 pool Collection,' was purchased by Herbert Thomas, Esq., of 

 Bristol, and Mr. P. P. Carpenter. The latter gentleman 

 "selected from it as many specimens as might be required 

 (1) to illustrate the local-fauna of a known station at the 

 mouth of the Gulf of California ; and (2) to exhibit the 

 amount of variation, whether great or little, observed in com- 

 paring together large n-ombers of individuals in the various 

 species. The latter object appeared of no slight importance, 

 especially for the sake of inland naturalists ; who have usually 

 to depend on the very limited number of specimens which are 

 generally to be seen both in public and in private collections." 

 This series Mr. Carpenter presented to the British Museum, 

 on the understanding that it should be kept separate and 

 intact for the purposes above named, like the Cuban, South 

 American, and other local collections : he undertaking, at the 

 same time, to prepare a Descriptive Catalogue, which is here 

 printed. The descriptions of the Brj^ozoa, occupjnng the 

 first six pages, were kindly communicated by G. Busk, Esq. 

 P. E. S., &c. 



"The collection consists of about 8873 specimens (250.5 Bi- 

 valves, &c., and 6368 Univalves) mounted on 2530 glass tablets. 

 The number to the left refers to the species, that to the right 

 to the tablet in the Catalogue. The minute specimens are 

 fastened on strips of thin glass enclosed in test tubes. By this 

 mode of arrangement, both sides of the object can be seen 

 without disturbance." 



"The measurements (unless otherwise expressed) are thus 

 taken. In the bivalves ; long, from the umbo to the middle 

 of the ventral margin ; lat. from the anterior to the posterior 

 ends ; alt. the thickness of the closed valves. In the spiral 

 univalves ; long, from the vertex to the base ; long. spir. from 



