PLATYCEINIDiE. 653 



crowning vice of the descrijDtions manufactured in this way, and one neces- 

 sarily following the methods employed, is the frequent absence of any com- 

 parison with other forms. All we have in many cases is the assurance of 

 the author that the species is so unlike any other that a comparison is 

 unnecessary. We have found in practice that a declaration of this kind 

 is a badge of suspicion, and is one of the most common indications of a 

 synonym. 



BUBLINGTONENSIS aROUP. 



Dorsal cup moderately deep, cup-shaped ; plates rather heavy, and with- 

 out ornamentation ; arms long. 



Platycrlnus burlingtonensis 0. and Shum. 

 Plate LXIX. Figs. 8a, h, c, d, e, f, g, h, i. 



1S50. Owen and Shdmatid; Joura. Acad. Nat. Sci. Phila. (new series), Vol. II., Part 1, and 1852, U. S. 



Geol. Rep. of Wis., Iowa, and Jlinn., p. 589, Plate 5A, Fig. 5. 

 1873. Meek and Woethen ; Geol. Rep. Illinois, Vol. V., p. 452, Plate 3, Figs. 6a, b, c. 

 1881. W. and Sp. ; Revision, Part II., p. 70 (Acad. Nat. Sci. Phila., p. 214). 



Sjn. P. inornatus McChesney ; 1859, Description of New Species, p. 6. Figured in the Trans. 

 Chicago Acad. Sci., Vol. I., Plate 4, Figs. 3«, b, as P. btirliiigtonensis. 



Syn. P. exsertus Hale, 1858 ; Geol. Rep. Iowa, Vol. I., Part II., p. 539. 



Sjn. P. nodobracJiiatus Hall, 1858 (not 1861) ; ibid., p. 542. 



Sjn. P. nuchiformis Hall, 1858 ; ibid., p. 540. 



SjB. P. lawtus S. A. Miller, 1891; Geol. Surv. Missouri, Bull. 4, p. 17, Figs. 3 and 4. 



Of medium size or less. Calyx a little higher than wide in the adult, 

 width and length about equal in young specimens, the ventral disk occupy- 

 ing one fourth of the height. Dorsal cup bowl-shaped, slightly spreading to 

 the arm bases ; the base rounded in large specimens, more or less flattened 

 and proportionally shorter in smaller ones. Plates moderately thick and 

 without ornamentation ; the radials toward the facets somewhat thickened 

 or longitudinally convex, so as to give to the cup, as seen from below, 

 a slightly pentangular outline. Basi-radial and interbasal sutures a little 

 grooved. 



Basal cup saucer-shaped, its height equal to half the length of the 

 radials; the interbasal sutures rarely visible in the adult; the column facet 

 circular and but little impressed. Radials about as long as wide, in large 

 .specimens somewhat longer, in smaller ones a shade shorter; wider at the 

 top than at the bottom, the upper margins slightly incurving, and the 

 superior angles truncated, especially at the anal side, where they form a 



