THE NAUTILCS. 41 



Bowden horizon. The Montpelier limestone contains, as a rule, 

 little that is recognizable in the way of fossils except foraminifera; 

 hence any species which can be identified is of interest, and in the 

 present case the interest is increased by the unparalleled size, for the 

 genus, of the species concerned. The specimens referred to appear 

 to belong to the sub-genus Miltha or Psendomiltha of the Lucinidce. 

 It is absolutely certain that they belong to the genus Lucina, senso 

 lato, and probably to one or the other of the above-mentioned sub- 

 genera. The species, which may be provisionally named Lucina 

 megameris, is, so far as I am aware, the largest Lucinoid shell known. 

 It is equivalve, very inequilateral, the beaks being near the anterior 

 third, moderately convex, though somewhat flattened peripherally; 

 the cavity of the beaks rather shallow, the internal margins of the 

 valves smooth and entire, the lower posterior part of the valves pro- 

 duced, the anterior end rounded, short ; posterior adductor scars 

 small and high ; anterior scar low, narrow and loriform, produced 

 backward nearly to the vertical from the posterior scar. There are 

 no traces of the cardinal teeth, if any, but there were two feeble, 

 non-functional, posterior laterals, one on each valve. The disk is 

 more or less radiately striated and profusely punctate, as in many 

 other Lucinas. The greatest length of the cast, on a line drawn 

 from the umbo tangent to the posterior end of the anterior scar, is 

 235 mm.; the shorter line at right angles to the last, 230 mm.; the 

 diameter of the cast from side to side, G7 mm. The margins are 

 defective to the extent of half an inch or more in front and behind ; 

 the valves appear to have been not quite closed when the matrix 

 filled them, but the margin opposite the umbones appears to be 

 complete. Allowing 15 mm. for the thickness of the shell at the 

 umbones, which from the breadth of the impression of part of the 

 hinge-plate preserved seems reasonable, and the total length of the 

 valves would in that case have been 250 mm., or about ten inches 

 The largest Lucinoid shell heretofore recorded, Lucina (Pseudo- 

 milthci) gigantea Desliayes, from the Parisian Eocene, attains a 

 length of 98 mm., slightly less than four inches ; from which the 

 overwhelming superiority in size of the Jamaican species is evident. 



The cast, without extraneous matter, weighs seven pounds avoir- 

 dupois. 



With the exception of Hippopus and Tn'dacna, the shells of very 

 few, if any, of the teleodont bivalves equal or exceed the above 



