222 FOURTH REPORT — 1834. 



Great additions have been made to oar knowledge of the mi- 

 nute Polythalamous Cephalopoda by M. D'Oi-bigny, whose me- 

 moir on these animals, read to the French Academy of Sciences 

 in 1825, will be found in the seventh volume of the Ann. des Set. 

 Nat. He confirms the propriety of assigning them a place in 

 this class, to which they had been referred previously, more 

 from analogy than from any positive knowledge of their real cha- 

 racters. He has studied far more closely than any former ob- 

 server the structure and development of the shell in this group, 

 as well as in many cases the structure of the animal. He has 

 ascertained that the former is internal, or at least entirely 

 covered by a membrane, and destitute of a siphon ; and that the 

 latter is possessed of true arms, or tentacula, analogous to those 

 of the larger Cephalopoda. He considers these animals as 

 forming a large and well-marked group in the present class, to 

 which he assigns the name of Foraminifera. He is acquainted 

 with upwards of six hundred species, nearly half of which have 

 been discovered by himself. 



M. D'Orbigny has undertaken an arrangement of these shells, 

 which has led to a revision of that of the entire class of Cepha- 

 lopoda by himself and De Ferussac jointly. It is the intention 

 of these authors to publish an extensive work * on this class, 

 which D'Orbigny divides into the three orders of Cryptodi- 

 branchia, Siphonifera, and Foraminifera. In the first, the 

 shell is either monothalamous, or internal and rudimentary, 

 never polythalamous : in the second, polythalamous, external, 

 or partiall}' covered by the animal, which is capable of retiring 

 either wholly or in part within the chamber above the last sep- 

 tum; a siphon always continuous from one chamber to another: 

 in the third, the shell is polythalamous, and always internal ; 

 the last septum terminal ; no siphon, but only one or more 

 apertures causing a communication between the different cham- 

 bers t- It may be observed that this arrangement by D'Or- 



that it must have been produced by an animal whose eggs are of much greater 

 magnitude, and that therefore the Ocytho'e cannot he the true artificer of the 

 shell in question. Mr. Gray's communication on this subject, which is not yet 

 published, will shortly appear in the Proceedings of the Zoological Society. 



* Since this Report was read, I have seen the first three numbers of this 

 splendid work which have recently appeared under the following title : Mono- 

 graphic des Cephalopodes Cri/ptodibratiches, par AIM. De Feriissac et D'Or- 

 bigny. Paris, 1834, fol. The plates are extremely beautiful. The Ceph. 

 Siphonifera and the C. Foraminifera are to form the subjects of two other 

 distinct monographs. 



■^ The same year in which D'Orbigny brought forward his memoir, De H*in 

 published at Leyden an important treatise, entitled, Monographice Ammonile- 

 oruni et Goniatiteorum Specimen. In this work, which I have not seen, there 

 is said to be also a new arrangement of the Cephalopoda, and a similar division 



