. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. 354 Mr. Toulmin Smith on the Classification cretaceous series. I believe only one, B. digitatus*, is strictly common to all the beds, and that undergoes a modification of character in the lower ones. Some of the most marked forms are, as far as present observation has extended, peculiar to the lower of these beds. § a. Operti. Brachial folds closed at extremity. 1. Brachiolites tuberosus. PL XV. fig. 3. Membrane having an irregular and generally slight primary fold : brachial
. The Annals and magazine of natural history; zoology, botany, and geology. Natural history; Zoology; Botany; Geology. 354 Mr. Toulmin Smith on the Classification cretaceous series. I believe only one, B. digitatus*, is strictly common to all the beds, and that undergoes a modification of character in the lower ones. Some of the most marked forms are, as far as present observation has extended, peculiar to the lower of these beds. § a. Operti. Brachial folds closed at extremity. 1. Brachiolites tuberosus. PL XV. fig. 3. Membrane having an irregular and generally slight primary fold : brachial fold arranged subspirally around a wide central ca- vity, and at rather distant intervals, in tuberous sacs, broad and flattened at the head, with slight depressions in the middle of the head. Of this remarkable species I am fortunate in possessing four well-marked specimens, all of which were found by myself, though in very distant parts of the country, and they are the only spe- cimens I have ever seen. The form is striking. Rising from, apparently, a very short root, it attains a considerable height, one of my specimens being upwards of three inches high. The sacs usually project about four lines from the central cylinder, and are about four lines wide, though sometimes more, at their broadest part. They open by a broad and trumpet-shaped mouth into the central cavity, which is wide and open at the top. Thus the access of sea-water is freely maintained. A transverse section gives the accompanying figure, which will be at once distinguished from that seen in a similar section (see fig. G, p. 289) of Cephalites capitatus or of any other of that genus. pig, m. The figure (3. PL XV.), which is from a specimen carefully developed from the chalk by means of the needle, gives a complete idea of the species. A large part is broken away, and thus the inside, as well as the outside, is cleared out and displayed. Being, however, developed by this means, and the spe- cimen being one in
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