TETRANOTA HIPPOPUS. 43 



Dimensions.- — i it 



(No. 593 Roy. Scott. Mus.) (Young) 



Height of shell . . . 10-0 mm. . 8-0 mm. 



Width of whorl at mouth . . 180 „ . 7"5 „ 



Horizon. — Upper Ordovician : Drummuck Group. 



Localiti/. — Thraive Glen, Girvan. 



Remarks. — The specimens are poor, two of the three in the Geological Survey 

 Collection at Edinburgh being in the condition of internal casts of old shells, the third 

 specimen having part of the shell preserved. The single example in Mrs. Gray's 

 Collection is a young individual and accordingly has the lateral revolving keels 

 sharper, whereas in the older individuals they are almost obsolete. The cancellation 

 of the surface recalls T. hidorsata (Hall).' 



The co-types are in the Royal Scottish Museum, Edinburgh. 



4. Tetranota hippopus (Salter). Plate VIII, fig. 16. 



1866. Bellernphon hippopus, Salter, Mem. Geol. Surv., vol. iii, [>. 350, pi. ii b, fig. 2 ; ibid., 2a(l eJit, 

 (1881), p. 557. 



Specific Characters. — Shell subglobose, composed of low transverse whorls much 

 wider than high, with broad flattened dorsum divided into a gently raised median 

 portion bearing broad slit-band, and outer low, rounded convex lateral portions 

 separated from the median elevation by broad, shallow, revolving depressions. 

 Umbilicus large, open?; umbilical edges sharp or subangular. Slit-band with 

 faintly raised edges, and crossed by strong equidistant lunulge. Mouth with deep 

 U-shaped dorsal sinus and strongly arched lateral lobes. Surface of dorsum 

 ornamented with strong transverse, sublamellose, equidistant lines arching back 

 sharply to meet the slit-band at 20° — 80°, with 2 — 3 finer lines between them. 



Horizon. — Arenig Series. 



Localiti/. — Ritton Castle, west of the Stiper Stones, Shropshire. 



RemarJiS. — A fuller diagnosis than the above is not possible OAving to the lack 

 of perfect specimens. Salter's figure (o/;. cit.) gave a fair idea of the general 

 characters, but did not sufficiently emphasise the lobation of the dorsum. 



The description which he gave of the species was as follows : "B. latissimus, 

 uncialis, striatus, vix costatus, anfractu ultimo maximc dilatato, striis inequalibus 

 conspicuis. Carina lata prominens. Apertura paullulum contracta. Umbilicus 

 profundus." In addition he makes the following remarks : " Broad-involute, the 

 outer whorl very wide, and rather depressed on the back with something of a 

 furrow on each side of the broad band, which is rather prominent and well-defined 

 in all ages. Strise arched backward, every third or fourth one stronger than the 



1 Ulricli aud Scofield, op. cit., p. 877, pi. Ixv, fig. 16 



