(i) 20 Palivontuhxila Sinica Ser. B 



Horizon and Locality: In the upper Machiakou (Actinoceras) limestone of 

 Tangshan, associated with Lopho^pira, Pagodispira etc. Collected by Geo. B. Barbour. 

 Only a single right valve of this species is so far known, this showing the interior, while 

 the characters of the exterior are not visible. 



The genus Cfeuodoi/ta is abundant in tlie Upper Ordovician of Nortli America, 

 M'here it is represented l.iy many species. From Chinese rocks Ctenodonta has heretofore 

 been reported only from the Lower Ordovician of Pupino in western Yunnan (Cowper- 

 Reed) but the species has not been identified. 



Class GASTROPODA* 



Order Rhipidoglossa Troschel 

 Family EUOMPHALID^E de Koninck 



Genus Ophileta A''anuxem 

 Ophileta plana Grabau (sp. nov.) 



Plate II, figs. 1, 2a -b. 



Shell -with the spire flattened to a plane, except for a faint sub-marginal keel, the 

 effect of which is to give the upper sui'face of the A\horl, i. e. the shoulder, a faint 

 concavity. There are about six volutions in what appears to be an adult specimen, the 



* It is dpsirable to define the various terms here used somewhat more precisely, since there is some variation in their 

 use. Sjiire is used in the usual sense for the spirally coiled portion of the shell above the last or hodij-v:]uirl. The angle formed 

 by the convergent sides of the spire is the aju'cul migle, the body-whorl being excluded where this enlarges more rapidly, or is 

 separated from the earlier whorls. Whorl is used in a general sense for the elements of the spire and for the last or 'body-whorl. 

 Voltilion is used more precisely for a complete coil, indicated by the lines of growth in juxtaposition on the two adjoining 

 whorls. When the number of whorls is given it refers to the number of coils in the shell counted upwards from the body-whorl. 

 In speaking of the first, second, third vululioii, or when the statement is made, that such and such a change occurs at the end of 

 3 1/2 volutions, or 4 volutions etc. the measurement is always from the apical point or protoronch of the shell, the first volution 

 being completed by the line of growth opposite (next below) the apical point. The whorls are separated by the Ktilnres. A 

 sHtiirnl shelf is a flattening of the succeeding \vhorl below the suture. The xiihsntnrnl xjn'ral or rarina lies at the upper edge of 

 the next lower whorl, next below the suture. A xnlui'al i-nnal is a depression at the suture, a sunken sutural shelf. S2}irals are 

 fine revolving ridges, a f<irliia is a thickened revolving ridge, which may be a single thick spiral or composed of several spirals. 

 It generally forms an aiifjnlatioit in the shell whorl. The strong angulation of the whorl next below the suture, is called the 

 shoulder anglr, and is measured in degrees. It is often emphasized by the peripJu'rul curlim, and forms commonly the most 

 salient feature of the whorl. The space between the shoulder angle and the suture is the sltmilder and it is usually flat or gently 

 concave or faintly convex. It may slope upwards as in Jjiplmxjiira, at right angles to the axis of coiling as in Oji/iileta and 

 }f<i(:lan'a or downward, and inwards, when the spire is drprrsxi-d, as in Er.cijliopierux. The part below the shoulder angle is the 

 hodij of the ichorl and it may contain one or more lourr curiinr each forming as a rule an angulation. They are numbered from 

 the shoulder angle downwards (forwards), lliha or cuMa- are transverse rounded elevation marking temporary expansions of the 

 whorl followed by an equal contraction. If the expansion is suddenly abandoned, so as to leave an open forward-pointing or 

 flaring portion of lip exposed, this is called a rari.r. It may be spinose, and it may be confined to a single spine at the shoul- 

 der angle. 



The degree to which the next whorl covers the preceding is called the amount of nnbracimj of the whorls. When 

 the amount is small, so that most of the preceding whorl shows, the spire is said to be hiose-cudnl, if much is covered, it is 

 close-coded. If the whorls become separated from the earlier ones they are said to be JujIij coded. Lax coiling begins with the 

 formation of a sutural canal or channel. In trochiform shells the embracing extends to the shoulder angle. In a few forms 

 with sunken spire, it may extend above the shoulder angle. 



