BRACHIOPODA. 323 



1SS2. Produetus, Whitfield. Bull. Amer. Mus. Nat. Hist., vol. i, No. 3, pp. 46, 47, pi. vi, fig.s. 6-12. 



1882. Productiis, "White. Eleventh A.nn. Rept. Indiana State Geol., p. 373, pi. xlii, figs. 1-3. 



1883. Produetus, Hall. Twelfth Ann. Rept. Indiana State Geol., pp. 325, 326, pi. xxix, figs. 6, 7. 

 1883. Prod^ictus, Hall. Rept. N. Y. State Geol. for 1882, plates (xviii) 49 ; (xix) 50. 



1883. Productits, White. Twelfth Ann. Rept. U. S. Geol. Surv. Ten-., p. 132, pi. xxxvi, fig. 1. 



1884. Produetus, White. Thirteenth Ann. Rept. Indiana State Geol., pp. 122-126, pi. xxiv, figs. 1-11 ; 



pi. XXV, figs. 1-5 ; pi. xxvi, figs. 1-3 ; pi. xxvii, figs. 1-3. 



1887. Produetus, Herhick. Bull. Denison Univ., vol. ii, pp. 47-49, pi. ii, figs. 25-30. 



1888. Produetus, Herrick. Ibidem, vol. iii, pp. 31-34, pi. i, figs. 24, 26 ; pi. iii ; figs. 20, 22-24 ; pi. 



vii, figs. 11, 20 ; pi. x, fig. 6, vol. iv, pp. 19-23, pi. iii, figs. 15, 17, 19 ; pi. 

 X, figs. 24, 25 ; pi. xi, figs. 26, 29. 

 1888. Produetus, Kbyes. Proc. Acad. Nat. Sci. Phila., Exti'act, pp. 6, 7. 



Our knowledge of the generic characters of this group has not greatly pro- 

 gressed during the last forty years. Though with the advance of investigation 

 the specific representation of the genus has become enormous,* the generic 

 value of Productus was nearly as well understood, if not so closely restricted, 

 at the date of the elaborate discussions of the genus by de Verneuil (Geologic de 

 la Russie, etc., 1845), and de Koninck (Monographie du genre Productus, 1847), 

 as at the present time. The generic divisions which have been since proposed 

 for species then referred to Productus seem to have but limited value or to 

 represent no fundamental variation from the type of the old genus. The fol- 

 lowing diagnosis can not, therefore, vary materially from those given by earlier 

 writers.f 



Diagnosis. Shell free, concavo-convex, the valves usually produced anteriorly; 

 outline semicircular, sometimes transversely elongate. Pedicle-valve convex, 

 sometimes geniculated, occasionally with a median sinus. Cardinal extremities 

 frequently auriculate. Umbo inflated, with apex incurved. Hinge-line straight, 

 cardinal area and teeth absent or rudimentary. External surface usually with 

 more or less prominent radiating ribs which are crossed, especially in the 

 umbonal region, by concentric lines or wrinkles ; rarely smooth or finely striated, 

 often studded with spines varying in size and abundance. These spines are 



* De Koninck described sixty-one sjiecies in his Monograph in 1847, not recognizing the genus Stropha- 

 LOSIA, King, 1844, nor indicating the vai'ious subdivisions which subsequent writers have erected into genera 

 or subgenera. In Miller's North American Geology and Palseontology (1889) eighty species of Productds 

 and twenty-seven species of Productella ai'e given as occurring in the Palaeozoic rocks of this continent 

 alone. 



t Waagbn, after his elaborate study of the species of the Productus limestone of India (1884), says : 

 "I have nothing new to add to them [the generic characters]." 



