PEKTCYCLUS TKAPEZOIDALIH. 14.-) 



tliL' edges of all the imier whorls, about three-eighths of the diameter of the shell 

 ill width, with subangiilar margin and nearly vertical sides. Whorl subtrapezoidal 

 in cross-section, about as high as wide ; indented to about one-fourth of its height 

 l)y the preceding whorl ; periphery narrowly convex, imperfectly defined ; sides 

 feebly convex, a little flattened near the umbilicus, and l)ecoming more flattened 

 and convergent on the body-chamber ; umbilical zone well defined, narrow, almost 

 perpendicular to the plane of symmetry of the shell. Body-chamber occn])ying 

 nearly a complete whorl ; aperture not seen, but the peristome (judging l)y the 

 lines of growth) probably with a broad, feeble lateral crest and a fairly deep hypo- 

 nomic sinus. Depth of chambers not seen; suture-line only imperfectly seen. 

 Test ornamented ^vith narrow, prominent ribs, which pass obliquely backward from 

 the umbilical margin, cross the lateral area in a feeble anteriorly convex cm've, and 

 form on the periphery a fairly deep and wide hyponomic sinus ; interspaces flat, 

 nearly twice as wide as the ribs ; the whole surface of the ril)s and interspaces 

 (when well preserved) with fine, close-set lines of growth, especially on the body- 

 chamber. The outer whorl with numerous (nine or ten) constrictions, following 

 the course of the ornaments of the test. ' Wrinkle-layer ' composed of fine, regu- 

 lar, close-set lonsntudinal Ihies." 



Dliiifini'ions. 



Unique specimen in 



Museum of Science 



and Art, Dublin. 



Diameter of shell ..... 141 mm. 



„ umbilicus (suture to sutm'e) . . 41) „ 



„ „ (edge to edge) . . . 53 „ 



Height of outer whorl . . . . 51 „ 



„ above preceding whorl (about) . . . 30 „ 



Thickness of outer whorl . . . . 50 „ 



Siijiplriiu'iitari/ Dencrijitioii. — Crossing the ribs and interspaces nearly at a right 

 angle, and thus rmming in accordance with the curvature of the whorls, are a series 

 of fine raised lines which may easily be seen in a favourable light by the naked 

 eye. On examining the surface of the test with a low magnifying power there is 

 a decided appearance of these lines having formed nodes in crossing the ribs, but 

 the condition of preservation makes this point a doubtful one (PI. XXXTX, fig. 2 c). 



The highly oi'nate character of the test in this species will make it easily recog- 

 nisable should other specimens fall into the hands of collectors. 



Owing partly to distortion, partl}^ perhaps to the grinding of the surface in tlie 

 effort to develop the sutures having been carried too deep, the latter are not satis- 

 factorily showu, but their general jjlan can very well be seen (PI. XXXIX, fig. 2 r/). 



