79 
mesial fold; the hinge-plate divided, and supporting two large conical spires which are 
directed into the hollow of the dorsal valve. 
Two species of this genus, viz., A. reticularis {Linn.), and Atrypa spinosa (Hall), (if, 
indeed, the latter is truly distinct from the former) are known to me as occurring in-the Cor- 
niferous and Hamilton Formations of Western Ontario. 
94, ATRYPA RETICULARIS (Linnzus). 
Anomia reticularis (Linnzeus), Syst. Nat., Hd, XII., p. 1132. 
A trypa reticularis (Dalman), Vet. Ac. Handl., Pl. IV., fig. 2. 
Terecbratula prisca (Vou Buch), Ueber Terebratula, p. 71. 
Terebratula ( Atrypa) prisca (Phillips), Pal. Foss. of Cornwall, &c., Pl. XXXIIL., fig. 144. 
Spirigerina reticularis (D’Orbigny ), Prodr. de Paléont., Vol. I., p. 99. 
Atrypa reticularis (Davidson), British Foss. Brachiopoda, Introduction, Pl. VIL, figs. 87— 
93, and Part VI, p. 53. 
Spirigerina reticularis (McCoy), Brit. Pal. Foss., p. 379. 
Atrypa reticularis (Hall), Pal. N. Y., Vol. IIL., Pl. XUIL., fig. 1, and Vol. IV., Pls. 
LI.,-LIIL, A. 
Atrypa reticularis (Billings), Canadian Journal, New Series, Vol. VIL, p. 264, figs. 84— 
87. 
(The above list comprises only the most important of the numerous synonyms of this 
persistent and cosmopolitan specics). 
Shell exceedingly variable, both in form and dimensions ; usually oblong-ovate, with the 
widest portion of the shell a little below the hinge-line. Ventral valve usually moderately 
convex in the vicinity of the beak, flattened towards the sides, and markedly depressed in 
front, with occasionally a broad but shallow sinus towards the front margin. At other times 
the anterior depression and sinus are inconspicuous. The beak of the ventral valve small, 
incurved, and so appressed to the dorsal beak as to conceal the minute foramen by which it is 
perforated. Dorsal valve always convex and uniformly more so than the ventral valve, though 
sometimes only slightly so; usually very gibbous, but becoming slightly concave towards the 
rounded cardinal angles, and for the most part without a defined fold corresponding with 
the sinus in the ventral valve. 
Surface covered with small radiating rounded ribs, generally two or three in the width of, 
a line, increasing by bifurcation and interstitial addition in proceeding from the beaks to the 
front margin. The radiating ribs are crossed by numerous concentric lines of growth, which 
usually form distinctly elevated or produced and squamose lines, and which, near the margin, 
are sufficiently close to give the ribs a characteristic nodose appearance. 
In the interior of the ventral valve is a broad mesial spoon-shaped depression, which 
gradually grows shallower in proceeding from the beak to the margin, and which is bounded 
by two well defined semicircular ridges, This gives origin chiefly to the divaricator muscles, 
and gives rise to a corresponding elevation, bounded by two semicircular depressions in the 
east ofthe valve. The interior of the dorsal valve is chiefly occupied by the greatly developed 
spiral supports of the arms. 
Atrypa reticularis ranges from the middle of the Silurian series to the summit of the 
Devonian, and is a well-known shell both in Europe and North America, In Western Ontario 
it occurs plentifully both in the Corniferous Limestone and the 5 ee Group. As a 
rule, the Corniferous examples are of larger size, and have more gibbous dorsal valves than 
those from the Hamilton series. An average Hamilton specimen has a greatest width of ten 
lines, its length being the same, and its height being five lines. An average specimen from 
the Corniferous has a greatest width of thirteen lines, A larger specimen from the same for- 
mation, with a more gibbous dorsal valve, has a width of fourteen lines, a length of eighteen 
lines, and a height of thirteen lines. 
Locality and Formarion.—Corniferous Limestone of Port Colborne, Ridgeway, Hlagers- 
ville, &e. Hamilton Group of Widder, and Bartlett’s Mills, near Arkona, in the Township 
of Bosanquet. 
