213 



remains very incomplete and unsatisfactory. About two hun- 

 dred nominal species have been described, and they appear to 

 inhabit temperate and warm seas, throughout the world, but are 

 absent in cold waters. Some tertiary species have been 

 discovered. 



Two of the principal works in which the Marquis de Folin 

 has described new species, namely, u Les Fonds de la Mer," and 

 "Annales Soc. Linn. Maine et Loire," xi, are unfortunately inac- 

 cessible to me. The former publication is particularly import- 

 ant for its illustrations. The Librarian of the Philadelphia 

 Academy has made several unsuccessful attempts to secure this 

 work through the Academy's agents in Europe, and I am reluc- 

 tantly compelled to do without it ; my monograph is therefore 

 necessarily very imperfect. On the other hand, I am able to 

 give illustrations of a number of species of Carpenter and C. B. 

 Adams hitherto unfigured. 



Genus CAECUM, Fleming, 1817. 



This is the only genus; the diagnosis consequently corres- 

 ponds with that of the family. Odontina, Zborzewsky, 1834; 

 Odcmtidium, Phil., 1836; Cornuoides, Brown, 1827; Brochus, 

 Brown, 1829; Cdecalium, Macgillivray ; Corniculina, Minister ; 

 Dentaliopsis, Clarke; Brochina, Gray, 1857, are synonyms. 



Costa has described the spiral portion only of the tube of a 

 Caecum, probably Caecum trachea, under the name of Spiro- 

 lidium Mediterraneum ; but he included a second species in his 

 genus, which appears to be a Parastrophia. 



The septum of the various species has a prominence upon the 

 external face, which is directed backwards and presents consid- 

 erable variation in form. 



Subgenus C^CUM, sensu stricto. 



Shell commencing with two or three whorls, planorboid (PL 

 66, figs. 41, 42), which are subsequently lost by truncation, and 

 the posterior extremity of the adult curved tube closed by a 

 diaphragm. 



Brochina, Gray, was founded on a single specimen, insuffi- 

 ciently characterized by its convex opercnlum. 



