16 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 5, 



globules which its chambers contain ; these globules or concretions, 

 which appear to have been produced by small vesicles, are not very 

 regular either in shape or number ; their existence might have been 

 considered as accidental, if several specimens had not presented the 

 same character. 



The shape of this Orthoceras is almost entirely cylindrical; its 

 length must therefore have been very considerable. The external 

 surface is completely smooth, whilst the interior of the air-chambers 

 is rough, and as if covered with shagreen. The chambers are regu- 

 lar, and the distance between the septa is equivalent to, or rather 

 more than, a fifth of the diameter of the shell. The siphuncle is 

 very large and central: I have not been able to assure myself 

 whether it is cylindrical or moniliform. 



The principal fragment observed possesses a length of 7 centi- 

 metres, and is composed of five equidistant chambers. The diameter 

 of the shell is 5 centimetres, while that of the siphuncle is 1^ centi- 

 metre. The test which forms the latter is about 2 millimetres thick. 



40. Orthoceras richiditjm, De Kon. 



The specimens representing this species are deprived of their shell. 

 The length must have been very great, the growth of the diameter 

 having been relatively feeble during the development of the animal. 

 The principal specimen, composed of eleven or twelve air-cells, of 

 the uniform length of 1 centimetre, measures 12 centimetres. Its 

 smallest diameter is 3^ centimetres, and its largest 4 centimetres. 

 ISTo ornament or sculpture can be seen on its surface. The siphuncle 

 is very large, and resembles that of the 0. cochleatum, Schl., to 

 which this species is closely allied. 



One of the specimens is accompanied by Productus semireticulatus, 

 Martin ; there can consequently exist no doubt as to its geological 

 age. From the Productus -limestone of Subbee. 



41. Orthoceras decrescens, De Kon. PI. VIII. fig. 4. 



Shell of a very elongated, conical shape. The internal cast alone 

 is known ; it has the surface entirely smooth, the transverse section 

 perfectly circular, and the siphuncle central and rather narrow. The 

 diameter of the terminal chamber is 2^ centimetres ; that of the 

 sixth chamber is 2 centimetres. The entire length of the specimen 

 is 12 centimetres, of which the last chamber occupies eight. The 

 five known chambers are remarkable on account of a regular decrease 

 in their length, so that, whilst the sixth chamber is 12 millimetres 

 in length, the fifth is but 10, and the second not more than 5. It 

 is this conformation, which I have seen in no other species, that has 

 suggested the name by which I have designated the one here de- 

 scribed. From the Productus-limestone of Moosakhail. 



42. Acrodus, n. sp. 



This species is very closely allied to Acrodus lateralis, Ag. It is 

 smaller than the one next described, of a much more elliptical shape, 

 and less transverse at its basis. From the coarse limestone of Che- 

 deroo. 



