1856.] SALTER — DIPLOCERAS. 381 



dorsal side upwards, like the recent Nautilus. In this case the 

 siphuncular side would be ventral. 



EXPLANATION OF PLATE VI. 



Fig. 1. Section of an Orthoceras from China ; representing the apical portion 

 [divided on the plate], and two out of the seven last air-chambers in 

 which no alteration had taken place. 

 a, a, air-chambers ; b, b, the same contracted ; e, c, intra-mural spaces ; 

 s, siphuncle ; t, membranous tube. 

 In the British Museum. 

 Fig. 2. Apex of a small Orthoceras {0. conicum, His. ?) in red limestone ; showing 

 the septa alternating with more strongly curved lines of the collapsed 

 lining membrane. Locality unknown. 

 In the British Museum. 

 Fig. 3. Section of Actinoceras Lyonii, Stokes, from the Black-river Limestone 

 of New York ; the membranous siphuncle and the tubes leading from it 

 to the contracted air-cells are fiUed with black marble ; the empty 

 spaces with white spar. 



In the British Museum. 

 Fig. 4 a. Fragment fi'om near the apex of an Orthoceras (0. striatum, Sby. ?), 

 from the Carboniferous Limestone of Ireland ; the surface is broken 

 away, showing what appears to be a large internal siphuncle. 

 Fig. 4i. Section of the same specimen, showing the small central siphuncle and 

 the line of separation of the internal membranes from the shell-wall. 

 In the Cabinet of Prof. Tennant, 

 Fig. 5. Siphuncle of Orthoceras trigonale, d'Arch. and Vern. ; magnified 2^ dia- 

 meters ; from the Devonian of Gerolstein. 

 In the British Museum. 



4. On a New Genus q/ Cephalopoda, Diploceras (Orthoceras 

 bisiphonatum of Sowerhy) ; and on the occurrence q/ Ascoceras 

 in Britain. By J. W. Salter, Esq., F.G.S. 



(Abstract.) 

 [The publication of this paper is deferred.] 



In this communication the author pointed out the apparent relations 

 of this peculiar form, which has been figured in the * Silurian 

 System ' and in * Siluria.' It possessed ordinary septa, pierced by 

 an excentric beaded siphuncle, and also had a deep lateral cavity 

 (supposed hitherto to be a second siphuncle) passing down side by 

 side with the siphuncle, and affecting at least seven, if not more of 

 the uppermost septa. 



Mr. Salter remarked that the structural peculiarities of Ortho- 

 ceras paradoxicum and of Gonioceras might offer some analogy with 

 the shell in question ; but he thought that the real affinities were 

 with Ascoceras and Cameroceras. 



Mr. Salter also described a new species of Ascoceras (A. Ba?'- 

 randii)^ found not long since in the Upper Ludlow rock, at Ludlow, 

 and at Stansbatch in Herefordshire. The genus is new to Britain. 



2 D 2 



