. Elements of conchology / Prepared for the use of schools and colleges. Mollusks. Fig. 74. CALYPTRiEA. 24. The CahjptropiB have in the interior of the shell, in form of a hollow cone, a small plate pro- jecting downwards, which seems to be the com- mencement of a columella, and is embraced in a fold of the abdominal sac; their branchice are composed of long slender filaments like hairs.— In some of them the plate or lamina adheres to the bottom of the cone, being itself bent into a portion of a cone or of a tube, and descending vertically. 25. The Siplionaria deserve notice, because they show
. Elements of conchology / Prepared for the use of schools and colleges. Mollusks. Fig. 74. CALYPTRiEA. 24. The CahjptropiB have in the interior of the shell, in form of a hollow cone, a small plate pro- jecting downwards, which seems to be the com- mencement of a columella, and is embraced in a fold of the abdominal sac; their branchice are composed of long slender filaments like hairs.— In some of them the plate or lamina adheres to the bottom of the cone, being itself bent into a portion of a cone or of a tube, and descending vertically. 25. The Siplionaria deserve notice, because they show how much the organization of mollusks may vary with- out any very striking difference in the form of their shell. Until recently these animals have been ranged with the patellae, to be descrihed in the sequel, which they resemble in their shell, but differ from them very much in the structure of their most im- portant organs: their branchia is composed of a few leaflets transversely attached to the bottom of a respiratory cavity, which is on the back, and communicat- ing externally by a lateral hole in the mantle; they do not appear to possess tentacles, but have a narrow veil on the head. 26. The genus Sigaretus {fg\ 75) has a flattened shell, with a slight spire, and a very large aperture, which is concealed in the Fig, 75.—SIGARETUS. ORDER OF GiLSTEROFOBA TUBUIiIBRA17C£XIATA. 27. Tubulibranch gasteropods are very analogous to the peclinibranch gasteropods, but are distinguished from them by very important differences in the organization of some of their organs, and in the structure of their shell, which is fixed to sub- marine bodies, and is in the form of a more or less irregular tube, the commencement of which only is spiral. It is divided into the genera Vermetus, Magilus, and Siliquaria. 24. What are the characters of the genus Calyptrae'a? (Calyptrae'a, from the Greek, kaluptra, a hood.) 25. What are the characters of the genus Siphona'ria ? 26. What are
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectmollusks, bookyear184
