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GASTEROPODA OF THE INFERIOR OOLITE. 



Bibliography, Sfc — It is unnecessary to repeat what has already been intimated 

 with respect to this species when dealing with Cirrus Leachi. 



Description. — The following are the proportional dimensions of the shell 



figured (spire restored) : 



Length (/. e. height) . . . .32 mm. 



Height of body-whorl to total length . . 50 : 100. 



Ratio of height to width . . . 62 : 100. 



Opening of the spiral angle . . . 30°. 



Mean spiral angle of shell . . . 120°. 



Shell sinistral, conical-depressed (subdiscoidal), widely and deeply umbili- 

 cated. The spire is conical-elongate, having towards its upper part an angle 

 of 30° — 35°. The precise apical conditions are unknown, but there is no reason to 

 doubt that the earlier whorls are flat, as in C. Leachi, costate or reticulate, close 

 and not turrited. 



When this earlier stage is concluded, with an entire change of shape the 

 nodose character of the whorls becomes more and more conspicuous. By sudden 

 bounds the whorls begin to increase outside the apical angle, and the anterior 

 whorls, including the body-whorl, expand into a broad discoidal shell with 

 canaliculate sutures. The ornaments in this stage are somewhat variable, but the 

 main feature is a central keel at the angle of each whorl, which is grossly tuber- 

 culated in connection with axial costae. 



The body- whorl expands greatly, so as partly to enclose the preceding whorl. 

 It somewhat resembles a tube, angular externally, circular internally. Thick costse 

 occur at regular intervals on the upper surface ; at the upper angle of the tube 

 these costse thicken into a series of knots which constitute the first or uppermost 

 spiral ; a short distance below this is a subsidiary spiral on the flank of the shell, 

 and below this again the ribs cross a clear space until they reach another spiral, 

 which is subsidiary to the row of nodosities (fourth spiral) at the lower angle of 

 the tube. In the base is a fifth tuberculated spiral (row of nodes) at the edge of 

 the umbilicus, which is enormous both in width and depth. The aperture is 

 circular, adherent, and expanding considerably towards the peristome. 



In the Coker specimens the finer ornamentation is rarely preserved, but we see 

 traces of closely-set curved growth-lines decussating with extremely fine spiral lines. 



Relations and Distribution. — This very remarkable species seems to stand 

 alone, though probably its nearest relative is Cirrus Leachi. But I fail to detect 

 in collections obviously intermediate forms. The short spire, discoidal aspect of 

 the shell, and tubiform shape of the body-whorl will usually serve to distinguish 

 C. nodosus from any other species of Cirrus. As far as appearances go, the 

 form of this shell would seem to justify Sowerby's idea that there was a connec- 

 tion between Cirrus and Euomphalus. 



