GASTROPODA. 8338 
Archinacella semicarinata.] 
Formation and locality Trenton group, Clitambonites bed, near Cannon Falls and Kenyon, 
Minnesota. 
Collections.— Geological and Natural History Survey of Minnesota; Geological Department, University 
of Minnesota; E. O. Ulrich. 
Museum Register, No. 7416. 
ARCHINACELLA SEMICARINATA, 2. Sp. 
PLATE LXI, FIGS. 12 and 13. 
Shell small, obliquely subconical, elliptical in outline; apex submarginal, small, 
scarcely incurved in the cast; dorsum obtusely carinate for a short distance from 
the apex, lateral slopes slightly flattened; hight of shell (the posterior part especially) 
less than usual, equalling about two-fifths of the width, the highest point just 
behind the apex. Surface nearly smooth. Length 12.5 mm.; width 10 mm.; hight 
4mm. Five specimens. 
The dorsal angulation allies this species to A. patelliformis Hall sp., but it does 
not extend backward so far, the apex is much smaller and less incurved, and the 
whole shell more depressed than in that species. It is distinguished in a similar 
manner from A. valida. 
Formation and locality—Trenton group, Clitambonites and Fusipira beds, Goodhue county, 
Minnesota. 
Collections.—H, O. Ulrich; W. H. Scofield. & 
ARCHINACELLA SIMULATRIX, 7%. Sp. 
PLATE LXI, FIGS. 10 and 11. 
Shell small, aperture horizontal, subovate, somewhat wider in front than 
behind; apex incurved, just above or projecting slightly beyond the anterior margin; 
back high, sharply rounded, the lateral slopes flattened. Surface markings obscure, 
concentric. Two specimens, one from Minnesota, the other from Kentucky. The 
dimensions of the former are as follows: length 10.5 mm.; width 8.5 mm.; greatest 
hight 3.4 mm.; hight of apex 1.7mm. In the other the same measurements give 
15, 12.5, 5.5 and 2.8 mm. 
This species is distinguished from A. deleta, A. valida, A. semicarinata and A. 
patelliformis in having a less regularly elliptical outline, the anterior half being wider. 
In this particular it is like the much larger A. cingulata. 
Formation and locality.—Black River group, Phylloporina bed, St. Paul, Minnesota; Trenton group, 
Modiolodon bed, Frankfort, Kentucky. 
Collection.—E. O. Ulrich. 
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