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PRODUCTA costata, 
TAR. DL X.—fig. 1. 
Spec. Char. Transversely oblong, with an angu- 
lar depression in the middle, costated ; costae 
few, broad, decussated at their upper parts, 
compressed upon the deflected front ; each 
side furnished with two or three spines and a 
small lobe. 
Strong, sulci divide the surface of this shell into 18 
broad ribs, which are crossed by concentric furrows upon 
the upper part of the convex valve : at each side is 
formed a small lobe, upon which are two or three spines : 
the front is much produced and deflected. 
For the use of this strongly marked Producta w r e are 
indebted to Mrs. Murchison. It was found near Glas- 
gow; and seems to have been imbedded in a shaley 
Limestone. 
PRODUCTA calva . 
TAB. DLX—figs. 2 to 6. 
Spec. Char. Nearly square, smooth, flat or con- 
cave in the middle; beak much incurved; one 
row of spines on each side the hinge-line. 
Var. 05. Small, flat or slightly concave in the 
middle, fig. 2. 
Var. (3. Twice the size of var. a, with a canal 
along the middle, figs . 3—6. 
iifXTE Anally this species is remarkably smooth ; but, 
like many others, it is scabrous within, or beset with 
