(i) 20 Palscontologia Sinica Ser. B 



HORIZON AND LOCALITY: In the upper Machiakou (Actinoceras) limestone of 

 Tangshan, associated with Lophospira, 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 Ctenodonta is abundant in the Upper Ordovician of North America, 

 where it is represented by 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 l>een identified. 



Class GASTROPODA* 



Order Rhipidoglossa Troschel 



Family EUOMPHALID^E de Koninck 



Genus OPHIL.ETA Yanuxem 



Ophileta plana Grabau (sp. nov.) 



Plate IT, 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 surface of the whorl, i. e. the shoulder, a faint 

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



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

 use. Spire is used in the usual sense for the spirally coiled portion of the shell above the last or body-u-horl. The angle formed 

 by the convergent sides of the spire is the apical angle, 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 (he elements of the spire and for the last or body-whorl. 

 Volution 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 volution, 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 npical point or protoconeh 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 siituret. A 

 siiiural shflfis a flattening of the succeeding whorl below the suture. The subsiitural spiral or earina lies at the upper edge of 

 the next lower whorl, next below the suture. A giiliti-al canal is a depression at the suture, a sunken sutural shelf. Spirals are 

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

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

 shoulder angle, and is measured in degrees. It is often emphasized by the peripheral earina, and forms commonly the most 

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

 concave or faintly convex. It may slope upwards as in I^ophospira, at right angles to the axis of coiling as in Ophileta and 

 Maclurea. or downward, and inwards, when the spire is depressed, as in Efcylioplcrm. The part below the shoulder angle is the 

 body of tilt whorl and it may contain one or more lower earinir each forming as a rule an angulation. They are numbered from 

 the shoulder angle downwards (forwards). Bibs or cosbc are transverse rounded elevation marking temporary expansions of the 

 whorl follow-ed 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 embracing of the wborls. When 

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

 close-coiled. If the whorls become separated from the earlier ones they are said to be la.rly coiled. 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. 



