CALYPTRiEID^. 109 



[Genus HARTTIA, Walcott, 1884. 



A cast indicating a patelliform shell within which extends a 

 low broad ridge, originating at one end and supports a broad, 

 subc'ordate shield-like expansion covering most of the other end. 

 H. Matthewi, Walcott (Pi. 30, fig. 1), Cambrian, St. John, N. B. 

 A group of doubtful affinities.] 



The following extracts from a lecture by P. P. Carpenter, 

 delivered under the auspices of the Smithsonian Institution, and 

 printed in its Annual Report for 1859, scarcely require apology 

 for their introduction here, in view of their intrinsic interest. 

 Carpenter and Dr. Gray agree in making large reductions from 

 the number of published species, although, as a matter of course, 

 they differ somewhat in detail. 



" The Calyptrseids (' slipper ' and ' cup-and-saucer ' limpets) 

 found on the Spondylus valves are the most beautiful and varied 

 that are known in any part of the world. The shells are large 

 and thin, delicately furrowed and as it were engine-turned, with a 

 profusion of tubercles, which sometimes rise up into long hollow 

 spines. The colors vary from white to a rich black-brown, or 

 are variouslj^ mottled with sienna, while the shape may be either 

 an elevated cone or a widel}' spreading disk. Sometimes the same 

 individual will begin with one form and sculpture-pattern, and 

 suddenly change to another ; others again seem to develop per- 

 manent and widel}^ differing varieties. Occasionally a starved or 

 diseased Mazatlanian will present the aspect which is normal on 

 the colder shores of South America ; exchanging its thin texture 

 and delicate sculpture for a coarse, solid, and nearly smooth 

 shell. So far the views lately propounded with such abilit}'^ by 

 the celebrated author of the ' Voyage of the Beagle ' meet with 

 sufficient confirmation ; and yet amid all its changes, there is a 

 habit of growth, hard to describe and yet easily recognized by 

 the practiced eye, which not onh^ unites the most aberrant forms, 

 but at once separates them from neighboring species found on 

 the same coast and appearing very similar to the common ob- 

 server. The ordinary plan of only preserving in collections a 

 few picked specimens displaying marked peculiarities, is by no 

 means favorable to the elimination of truth in reference to spe- 



