70 MISS J. DONALD ON MICRENTOMA. [Feb. T898, 



higher part of the r^pire ; they gradually become sinuated, till on the 

 lower whorls a sinus is formed, the filling up of which produces a 

 band. This band is absent from the higher whorls, which are quite 

 smooth. PseudomurcJiisonia is further distinguished by having the 

 sinus in the widest part of the whorl. 



The type of this genus is M. [Aclisina'] nana, De Kon., which is 

 at present the only known species. 



MicEENTOMA NANA (De Kou.). (PI. Y, figs. 12 & 13.) 



Aclisina nana, L. G. De Kouinck, 1881, ' Faune Calc. Carb. Belg.' Ann. Mus. Roy. 

 Hist. Nat. Belg. vol. vi, pt. iii, p. 87 & pi. vii, figs. 29 & 30. 



Description. — Shell small, conical, composed of more than nine 

 whorls. Protoconch unknown. Whorls flat above, slightly convex 

 below, becoming more convex as they increase in size. Whorls 

 ornamented by six strong, crenulated spiral threads, only four or 

 five of which are visible on the upper whorls. Crenulations so 

 strong as sometimes to form by their confluence longitudinal ribs, 

 which follow in general the course of the lines of growth. The 

 lines of growth indicate a slight notch in the outer lip, which 

 apparently becomes rather deeper in the mature state; it is situated 

 between the second and the third threads from the upper suture, and 

 there is sometimes a very fine thread down the middle of this space. 

 Sutures of moderate depth. Base convex. Aperture imperfectly 

 known, probably subovoid. Columella simple, slightly oblique, 

 thickened. Umbilicus closed. 



HemarJcs. — I have seen the specimen marked as the type of this 

 species in the Brussels Museum ; it is very small, having nine 

 whorls in a length of 3| mm. It is embedded in the limestone 

 matrix, and somewhat distorted by pressure. It agrees, however, 

 with the British shells referred to this species in character. The 

 locality is Vise (Assise YI). There are also several larger individuals 

 from the same place in the Museum at Liege. On one the longi- 

 tudinal ribs are so strong on the upper whorls that it somewhat 

 resembles a species of Loxonema^ but on the last whorl these ribs 

 become less strong, and the lines of growth give distinct evidence of 

 the notch in the outer lip. M. le Chanoine de Eorlodot has a single 

 example from Tournai in his collection. 



Resemhlances. — This shell resembles Aclisoides striatuIa^De Kon., 

 in general appearance, but it may be distinguished by the whorls 

 being less convex, the ornamenting threads stronger, fewer, and 

 decidedl)^ crenulated, and also by the lines of growth not forming a 

 deep sinus in the outer lip, but merely a notch. It bears a super- 

 ficial likeness to Pleurotomaria serrilimha, Phil.,^ from which it 

 differs in the spiral threads being more numerous and in possessing 

 a notch in the outer lip. 



Locality and Horizon. — There are six specimens in the Museum of 

 Science & Art, Edinburgh, from Park Hill, Derbyshire ; the apex 

 and base are imperfect in all. The specimen figured (PI. Y, fig. 13) 



^ ' Geol. Yorks.' vol. ii (1836) p. 228 & pi. xv, fig. 30. 



