734 DR. J. K. GRAY ON THE CALYPTR^ID^. [Juiie 2/, 



observation that Mr. Lovell Reeve made on the remarks that I 

 made respecting; the development of the shell of Humphreyia, " That 

 if the shell could speak it would be astonished at what was said 

 respecting its structure." 



When the structure of Trochifa, Cri/pta, Crucibulmn, and Mi- 

 trella are studied in a series, it is easy to understand and to trace 

 out how the various forms gradually pass into each other; and the 

 ])eculiarity by which the genera are separated is chiefly a modifica- 

 tion of the inner lip. And from analogy one is convinced that the 

 curved plate at the top of the cavity of Calyptra must be a modifi- 

 cation of the same part of the shell. As yet we have not discovered 

 any shells which show how the modifications have been brought 

 about, or which show any intermediate form betvi'een the plate and 

 the cup-like appendage of Crucibulum, or the spiral lamina of Mi- 

 trella, which is most developed in Trochita. It has been suggested 

 that it is half of the internal cup of Crucibulum : but this is a 

 mistake ; for the adductor muscle is attached to the outer surface 

 of the cup of Crucibulum, and to the front of the inner surfaces of 

 Calyptra ; so that, if it is any modification of that cup, it must be 

 that the two sides of the cup are compressed together, and the cup- 

 like concavity destroyed. We only know that the spiral shell that 

 covers the just-hatched animal, instead of being extended in its spiral 

 form, is developed into a nearly symmetrical conical shell without 

 the least appearance of a spire, and that the inner lip of the nucleus 

 is dilated into a curved subsymmetrical appendage attached to the 

 apex of the upper part of the cavity, to the front or inner surface 

 of which the adductor muscle which fixed the animal to the shell is 

 afiixed. 



As Trochita is the most spiral, and indeed exhibits the most normal 

 form of the shell of the family, so Calyptra is the most abnormally 

 formed shell of the group. The simple conical form of the shell 

 and its cavity gives it some resemblance to the shell of Capulus ; 

 and Calyptra differs from all the other genera of the family to which 

 it is referred by the animal forming an under valve or shelly plate, 

 as the animal of Ilipponyx does among Capulidce ; but the position 

 of the adductor muscle shows that the genus, though so abnormal, 

 is properly referred to Calyptrceidce. 



Tribe I. Shell conical, circular, spiral; apex central; whorls seve- 

 ral, regular ; nucleus spiral; cavity circular, spiral, with an 

 oblony four sided mouth. Trochitina. 



1. Trochita, Schumacher; Adams. 



Trochatella, Lesson. 

 Infundibulum, D'Orb. 



Shell conical, circular, spiral. Apex central. "Whorls several, 

 well developed. Base circular, concave. Mouth moderate, oblong, 

 four-sided, transverse. Axis central, imperforated, not exposed to 

 view. 



