114 SYNOPSIS OF THE CHARACTERS OF THE 



This species has tlie same general shape as the Producta scabricula, but is considerably larger; it differs 

 from it in having the entire surface covered by distinct, transverse undulations, which are quite smooth on the 

 ears and sides of the shell, but on the other parts bear small, lengthened, close-set tubercles. Length two 

 inches, width two inches and a quarter. 



Peoducta quincuncialis. Phil. 



Producta quincuncialis. Phil. Geol. York. 



,Sp. C/«.— Hemispherical; hinge-line exactly the width of the shell; front margin semicircixlar ; usually 

 without a mesial hollow ; surface witli coarse, longitudinal striae, swelling alternately into lengthened tubercles. 



This species is often confounded with the Producta scabricula, its nearest afSninity is, however, perhaps 

 to the Producta antiquata ; the structure of the tubercles is curious, and will, at any time, distinguish this 

 species from the Producta scabricula ; in the present shell they are merely a thickening, at intervals, of the 

 radiating ribs, while in the Producta scabricula they form distinct, unconnected tubercles, bearing at their 

 lower extremity a small spine. Stress is sometimes laid on the distinguishing character o£ Producta scabricula 

 having a deep mesial hollow, and the Producta quincuncialis being without one ; although this is generally the 

 case, yet specimens of Producta scabricula occasionally occur without a mesial hollow, and Producta quincun- 

 cialis as often has one. It never attains the same size as Producta antiquata, and may be distinguished by 

 having its front wider, and more nearly semicircular, its sides striated, its beak much more gibbous, and by 

 having the concentric wrinkles at the beak fewer, and never assuming the large, rugged, spinous character at the 

 sides, which we see in the Producta antiquata. Length one and a half inches, width two inches. 



Producta rug at a. Phil. 



Producta rugata. Phil. Geol. York. 



Sp. Ch. — Orbicular, depressed ; hinge-line short ; surface with few, large, irregular, concentric wrinkles, 

 and scattered spines ; no mesial fui-row. 



This scarce species is very much depressed ; the cardinal angles are flattened, so as to give something of an 

 eared appearance to the shell ; the concentric undulations are few in number, obtuse and irregular ; seldom ex- 

 tending more than half way across the shell ; the tubercles are large, scattered, and very few in number. The 

 length seven lines, width six and a half lines, depth three lines. 



Producta scabricula. Sow. 



Productus scabriculus. Sow. Min. Con Producta scabricula. Phil. Geol. York. 



Sp. Ch. — Semicircular, gibbous; mesial hollow wide; surface with numerous, oblong tubercles, arranged in 

 quincunx, each having at its anterior end a small spine, directed towards the margin. Length two-thirds the 

 width. 



This species has in general a wide mesial hollow, but specimens sometimes occur in which it is not visible ; 

 there are irregular, faint, concentric undulations ; the tubercles, when well preserved, are found to be the bases 

 of exceedingly small spines, which are placed at the end, next the margin of the shell ; the cars are rectangular 

 and wrinkled. Length one inch nine lines, width two inches four lines, depth one inch. 



Producta Scotica. Sow. 



Productus Scoticus. Sow. IMin. Con. — Producta aurita (pars.) Phil. Geol. York. 



Sp. Ch. — Semicircular, twice as wide as long; ears large, flattened, gibbous towards the beak; radiating 

 strias fine, obtuse, flexuous ; more or less wrinkled transversely ; the bases of cylindrical spines irregularly scat- 

 tered over the surface. 



