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Zoology. 285 
The nacreous or mother of pearl structure has been supposed to be® 
due to the cropping out of laminz in succession. But Mr. Carpenter 
finds that the iridescence is exhibited by the animal membrane after the 
calcareous matter is removed, and moreover that it belongs to a single 
layer of membrane, and is owing to a corrugation of the surface or a 
series of folds or plaits, which lie more or less obliquely to the general 
surface. 
Mr. Carpenter pursues the subject with great minuteness and skill, 
and ascertains characters from his investigations for determining the 
affiliation of groups. Characters also are afforded for distinguishing 
in many instances even ea a these characters it will be observed, 
are obtained from mere fragme 
3. On Belemnites, (Quarterly Tairesl of Geology, No. 1, p. 119.)— 
The Belemnite, whose connection with the Cephalopoda, or the cuttle- 
fish tribe, has been for some years determined, is regarded by Richard 
Owen, Esq., as forming a transition link between the two genera 
Sepia and Spirula, though uniting also some of the characters of the 
genera Sepiola and Onychoteutis. ‘The lateral fins of the Sepia are 
narrow, and extend from the apex of the mantle. to near its base, 
while the fins of the Belemnite were relatively shorter and broader, 
and situated a little in advance of the middle of the body. In the 
relative size, shape and position of the fins, the Belemnite must have 
most nearly resembled the species of the existing Rossia and Sepiola ; 
but it differed in the more elongated and slender body.” ‘*' The Belem- 
nite, with the advantage of its dart-shaped and well balanced shell, must 
have enjoyed the power of swimming backwards and forwards by the 
action of its cephalic and pallial fins, with greater vigor and precision 
than the modern Decapod Dibranchiata. The position of the animal 
was probably more habitually vertical than that of its recent congeners. 
Thus placed, the Belemnite, in quest of prey, would rise swiftly or 
stealthily to fix its claws in the belly of a supernatant fish, and then 
dart down to drag its prey to the bottom and drown ii. And we cannot 
doubt that the ancient Belemnites were in their day = most formidable 
and predaceous of Cephalopods.” 
4. Trilobites, (ibid., p. 182.)—Burmeister, in a late treatise on Tri- 
lobites, places these fossil Crustacea among the Entomostraca, and near 
the genera Apus and Branchipus. Dr. Burmeister, as has’ been done by 
other naturalists, suggests that the fossils are often only the fossilized 
exuvie, as these animals must have cast their exuvie like other Crusta- 
cea. Thesocalled genera Battus and Agnostus, he considers as young 
individuals of different species, in which state Crustacea often differ 
very widely from their adult forms. Dr. Burmeister concludes that 
they swam with the back undermost, and lived near coasts or in shallow 
waters. 
