Yol. 54.] MISS J. DONALD ON" ACLlSOrDES. 67 



the section Hypergonia, from which it diflPers in having less angular 

 whorls and in the sinus being situated on the widest part of the 

 whorl, instead of above it. In general appearance it comes very 

 near some of the recent Twrritelloe, especially such forms as 

 T. accisa, Watson, and T. runcinata, Watson, where the sinns 

 merely lies between the ornamenting carinse, not forming a distinct 

 band ; but the aperture is different here, being more quadrangular, 

 and the whorls also differ in being flatter. 



MUKCHISONTA [AcLISOIDES] STEIATTJLA, Do KoD. (PI. Y, figS. 6-8). 



Turritella striatula, L. Gr. De Koninck, 1843, ' Prec. Elem. de Geologie/ par J. J. 

 d'Omalius d'Halloy, p. 516. 



Murchisonia striatula, L. G. De Koninck, 1843, 'Descr. Anim. Foss. Terr. Garb. 

 Belg.' p. 415 & pi. xl, fig. 7; H. G. Bronn, 1848, 'Index Palteont.' pt. i, p. 748; 

 A. d'Orbigny, 1850, ' Prodr. Paleont. Stratigr.' vol. i, p. 122 ; ? J. Armstrong, 

 J. Young, & D. Robertson, 1876, 'Cat. W. Scot. Foss.' p. 56; J. J. Bigsby, 1878, 

 'Thes. Dev.-Carb.' p. 327; R. Etberidge, 1888, ' Foss. Brit. Is.' vol. i (Palaeozoic) 

 p. 302. 



Aclisina striatula, L. G. De Koninck, 1881, ' Faune Calc. Carb. Belg.' vol. vi, 

 pt. iii, p. 86 & pi. ix, figs. 57 & 58 ; 1883, vol. viii, pt. iv, pi. xxxiii, figs. 41 & 42. 



Description. — Shell elongated, conical, composed of more than 

 ten whorls. Protoconch consisting of one smooth, convex whorj, 

 simply coiled on the same plane as the rest of the spire. Whorls 

 moderately convex below, flat above. Ornamented by nine or ten 

 raised threads of irregular strength, separated by grooves varying 

 in width ; there are several additional threads on the bodj^-whorl. 

 Sutures not very deep. The lines of growth indicate the existence 

 of a sinus in the outer lip of moderate depth, situated on the widest 

 part of the whorl, near the middle of the body-whorl, but rather 

 below the middle on the whorls of the spire. It lies between two 

 threads, with generally a third thread between them. Aperture 

 ovoid. Base produced, convex. Umbilicus closed. 



Remarks. — There is always more or less variation in the strength 

 and arrangement of the ornamenting threads on different indi- 

 viduals; as a rule the lower threads are the strongest, and the 

 spaces between them the widest, but sometimes finer threads are 

 intercalated. The depth of the suture also differs, as some indi- 

 viduals are less compactly coiled than others ; this is especially 

 noticeable in two specimens from Yise in the British Museum (Nat. 

 Hist.), where the sutures are deeper than usual, owing to the whorls 

 being more exsert. 



Resemblances. — Micrentoma nana resembles this species to a certain 

 degree in the form of the whorls and in the compactness of the spire, 

 but it differs in not possessing a deep sinus on all the whorls, in 

 having the threads strongly crenulated, and in the threads being 

 more equal in strength and less numerous. 



Locality and Horizon. — There are nine specimens in the Wood- 

 wardian Museum, Cambridge, from the Carboniferous Limestone 

 (d^) of Settle. The largest of these has the apex broken, leaving 

 seven whorls, which have a length of 16 mm. That figured (PI. Y, 

 fig. 6) also has the apex broken ; six and a half whorls remain, whose 

 length =12 mm., width =:4| mm. The body-whorl of another is 



f2 



