OKTHOC'ERATIDA 



OBTHOKTX 



id by a simple nearly cylindrical ijphuncle, either 



tfc* month, pel 



m or not far removed from the 'cwtre of the disc (never marginal). 



a. Last chamber, cylindrical, at O. ffif^Hnm. 

 0. Last ebamber contracted towards the aperture, at O./iutfbrsu. 

 Ormem* (tVpM. a bead, combined with >ai). Stokes.-A straight 

 inmminliil shell, with septa as in Orftoomu, perforated by a 

 sjphMKfr similarly situated, but much dilated in each chamber, and 

 Mttltrtixl at the parts where the septa are attached to it. The inner 

 part of the siphuacU is divided into chamber., corresponding in num- 

 ber with the chamber., and deeply indented in the middle, where the 

 septa of the shell are attached to them ; to that one-half of each 

 division of the tiphuncle is in on* chamber, and the other half in tin 



. 



The typical species an from Drummond Island, in Lake Huron. 

 (Stokea, In 'OeoL Proceeding*, 1 1838. and 'OeoL Transaction*/ 1840.) 



Ariiitonrai (fcrvfr, a r*y, combined with *?*<), Stokea. A itnight 

 conical coocamerated shell, with eepta at in Ortkoctnu, and siphuncle 

 fill, at to its external face, u in Omoeeraj. Within the siphuncle 

 U a continnoiu tube, which appear* to hare been capable of expansion 

 and contraction, and U furnished with verticillate radii, which connect 

 the tube with the wills of the siphon. 



The species are from lake Huron and other part* in North America, 

 and Caetle Ernie in Ireland. 



u (Broun) u included in Actinoctreu (Stokes). 



CmtJfim (Miller). A .traight or .lightly bent (T) pyramidal 4-sided 

 QCMmerated (?) ahelL 



C. quudnnUata it a common ahell in what were called Transition 

 Rook* in Sweden, Wenlock, Dudley. Ac. ; and a similar species occurs 

 in the Carboniferous llocks of Coalbrook Dale and Kuthcrglen. 



it. In -lining the bent or partially convoluted Polytliaiamacta, we 

 may find advantage in attending to the situation of the siphuucle. 

 For example, the siphuncle U subdorsal or approaches the outer line 

 of curvature in Cyrtocerat (Ooldfuss) and Gynccrcu (Meyer); it is sub- 

 central in LttHtta (Breyn) ; and it U suboentral or approaches the 

 inner line of curvature in the genus Pkraymocerat (Broderip). 



The geological distribution of these forms is nearly as in the true 

 Orlkfttnlt. They are all peculiar to the strata below the new red 

 system; and mostly occur below the carboniferous or Mountain 

 Limestone. Pkraymoetnu prevails in the Ludlow Rocks ; Oj/rtocerai 

 specially abounds in the strata of South Devon, the Eifel, and the 

 Mountain Limestone; and Oyroctrat and Lituiia follow nearly the 

 Sam* rule ; a few species of Liluitei occur in the Silurian Rocks. 



(yrtocmu (mpr**, curved, and fipat, a horn), Ooldfuss. Bent, 

 arched, or partially convoluted, the free end being sometimes 

 elnnpted and straight Septal edges seldom free from a alight 

 waving ; aipbuncle subdorsal, or even marginal, seldom quite round ; 

 aperture nearly orbicular. 



C. dtfitmum if found in the KifeL 



Several other species occur in Devonshire, near Ludlow, Ac. 



N 



Ineurvwl, ><, a horn), Meyer. Coiled like a 

 tendril, to that the volutions do not touch. Septal edge even, siph 

 nacU dorsal, marginal, Aperture nearly round. 



O. grteHf, Meyer. Bronn, In ' Leth. Oeog.,' voL i. fig. 6. From the 

 States of Dillenburg. 



iMmiHt, Bnyn. Convoluted, to that the volutions touch in all the 

 inner part, but afterwards extended into a straight or brat portion. 

 Septa pierced by a subcentral riphuncle. Aperture nearly round. 



L. trtiamlflmt, Sowerby, U an example. 





I'kraymocerat 



septum, xipat, a horn), Broderip. Shell 



incurved and oomprentied, more or less conical ; septal edges entire, 

 crossed externally by the lines of growth ; siphuncle near the inner 

 margin ; aperture contracted at the middle, its outer extremity produced 

 into an elongated beak. Two figures are given below to show the 

 singular contraction of the aperture. 

 P. wtfnetMt*. Broderip, in ' Silurian Researches.' 



Fhrngmoctrai rentricoium. 



C. Among the completely spiral and convoluted Polythamacea, the 

 situation of the siphuncle and the form of the septa become useful 

 guide*. 



The siphuncle is dorsal in some Nautili of the Mountain Limestone, 

 which ought perhaps therefore to be distinguished ; subcentral in 

 most of the Nautili of the Oolitic, Cretaceous, and more recent 

 deposits, as well as in recent species ; ventral in Clymcnia (Muuster) 

 and in some otherwise true A'autili of the Coal Formation and 

 Magneeian Limestone. 



The septa are limply concave, with their edges even, in most 

 \autili ; but in some species (.Y. bilobatiu, from the Coal Formation 

 and Mountain Limestone) they are deeply undulated, as in the simplest 

 Clvmmia [QoHlATrrKs] ; iu a remarkable fosnil from the London Clay 

 (\autiltu Ziaac), deeply and angularly folded, nearly as in tome 

 Qoniatites. Finally, in the C'lymenia of Count Munster, all having a 

 ventral siphuncle, the septal edge is simply waved, or has rounded 

 inflexions, angular bands, or a mixture of these in the same shell. 



Taking a general view of the distribution of the PolyfoUamaeea we 

 find 



,Vn</.V,r i' 1 " 1 -V" '''/i'/i' 

 Some of the XatUilidee. 

 .\autilida, JMemnitidtr, Ammonitidtr. 

 Kavtilidae, lielcmnitiittr, Ammonitida. 

 f fi'autilida: (not including t>rthoccrata), 

 I Ammonitida: (of the type called Ceratitea 

 I only). 



Xa*tilid<t, including Cyrtocerata, Ortho- 

 cerala, Ammonitida (of the type called 

 I Qoniatites only). 

 ? \attlilidft (including Cyrtoctrala, Phrag- 

 mocerata, OrtAoeerute, and Clymenia) ; 

 In still Lower SI i . < A mmm itida of tho type of Qoniatites 



I. only. 



Finally, in strata lower than these, as the Snowdonian Slates, where 

 shells and Polyplarlan remains occur, none of the Polythalamacea are 

 known. [AMMONITES ; Or JALOFODA ; N ADTILID>K ; BELKIINITBS ; 

 BACOLITKS; BBU.KKOI-HOH.] 



O'RTHONYX, M. Temminok's name for a genus of Birds arranged 

 )>y Mr. Swainson with Snphaya under SupHayina; these two genera 



In a living state . . . 

 In the Tertiary Series . 

 In the Cretaceous Strata 

 In the Oolitic Strata . 



In the Saliferoos Strata 



I u the Carboniferous Strata 4 



