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XXIII. On the Anatomy of the Calyptreide. By Ricuarp Owen, Esq., F.Z.S., Assist- 
ant Conservator of the Museum of the Royal College of Surgeons in London. 
Communicated February 25, 1834. 
MY friend Mr. Broderip having, in the course of his examination of the shells of the 
family Calyptreide in the collection of Mr. Cuming, detected a series of gradations in 
the form and extent of the internal shelly plate, intermediate to those characterizing the 
species which have been proposed as types of subgenera, he requested me to examine 
the soft parts, and see whether a corresponding gradation prevailed in any of the or- 
ganic systems, or whether these presented differences sufficiently marked or constant to 
sanction the adoption of the proposed subgeneric divisions. 
Mr. Cuming’s collection and that of Captain King have afforded the necessary ma- 
terials for this investigation ; and although the difference between Crepipatella, Less., 
and Calypeopsis, Less., in the extent of the locomotive and respiratory systems is con- 
siderable, yet the intermediate or connecting species present gradations in the structure 
of these parts corresponding to those in the form of the shelly plate, the latter peculiar 
feature of this family of Gasteropods acquiring magnitude, for the purpose of protect- 
ing the visceral mass and of isolating it from the foot, in proportion as this part is 
better organized for extension and contraction. . 
The labours of Cuvier!, of M. Deshayes?, and of M. Lesson? have sufficiently eluci- 
dated the general plan of formation which pervades this family of Gasteropods. Their 
dissections illustrate the structure of the subgenera Crepidula, Calyptrea, and Crepi- 
patella respectively ; but the soft parts of Calypeopsis, Less., or Dispotea of Say, have 
never been figured or described ; and two large specimens of a species of this sub- 
genus‘, kindly presented to me by Capt. P. P. King, have afforded me the means of 
adding a few particulars to the amount of anatomical knowledge already possessed 
with respect to the Calyptreide. 
The internal shelly Jamina in that form of Calyptrea which M. Lesson has distin- 
guished by the name of Calypeopsis, is free in the whole of its circumference, forming a 
delicate cup-shaped shell, adhering by the base and nearly the whole of one of the sides 
to the outer large limpet-shaped shell. 
' Anat. de la Crépidule, Mém. des Mollusques. 2 Ann. des Sci. Nat., tom. iii ¢. 338. pl. xvir. 
* Anat. de la Crepipatella Adolphei, Zoologie de Duperrey, tom. ii. pt. 1. p. 292. 
* Calyptrea (Dispotea) Byronensis, Gray, Mus. Brit. 
