152 BRITISH CARBONIFEROUS BRACHIOPODA. 



American localities, such as at the Island of Quehaja, near the Lake Titicaca. at the foot of 

 the Bolivian Andes ; at Quincy, Illinois ; Keokuk, Iowa, &c. 



Puoductus costatus, J. de C. Soio. PI. XXXII, figs. 2 — 9. 



Probucta costata, J. de C. Sow. Min. Conch., pi. 560, fig. 1, May, 1827. 



— sulcatus, Sow. lb., pi. 319, Jan., 1822. 



— costata (et sulcata, Soiv.), Phillips. Geo], of York., vol. ii, pi. vii, fig. 2, 



1836. 



— costellatus, M'Coy. Synopsis, pi. xx, fig. 15, 1844. 



— costatus, De Vemeuil. Russia and the Ural Mountains, vol. ii, pi. xv. 



fig. 13 ■•»■ 1845. 



— — De Koninck. Mon. du genre Productus, pi. viii, fig. 3, and 



pi. x, fig. 3, 1847. 



— — Dav. Mon. of Scottish Carb. Brach., pi. ii, figs. 22—24, 



1860. 



Spec. Char. Shell very variable in shape, transversely semi-cylindrical, wider than 

 long ; hinge-line about as long as the width of the shell. Ventral valve gibbous, very 

 much vaulted ; abruptly arched, or obscurely geniculated ; beak incurved, but not overlying 

 the hinge-line except at its attenuated extremity, a median longitudinal sinus or depres- 

 sion dividing the valve to a greater or less extent into two lobes ; ears more or less 

 developed, sloping abruptly from the visceral portion, with a strong, rugged, semicircular 

 ridge on either side, obliquely placed to the hinge-line, and from which project several long, 

 cylindrical, hollow spines, similar to those situated close to the cardinal edge. Surface 

 covered with a variable number of strong, longitudinal rounded ribs of unequal width, and 

 which become more numerous towards the margin from occasional bifurcation or inter- 

 calation, while the whole visceral portion is crossed by numerous regular concentric wrinkles, 

 producing reticulate tuberculations. The spines are long, but variable in number, projecting 

 here and there from the ribs. Dorsal valve somewhat geniculated, following the curves of 

 the opposite valve, a slight median elevation corresponding to the sinus of the ventral 

 valve; the visceral portion is usually somewhat flattened, while the anterior portion of the 

 valve becomes more or less abruptly bent upwards, the sculpture being similar to that of 

 the opposite valve. 



Dimensions variable : a. typical specimen measured, length 13, width 23 lines. 



Obs. So variable do the shells composing this species appear to be, that it is verv 

 puzzling to know how to dispose of certain shapes which, although individually somewhat 

 different from the typical form, appear, nevertheless, linked to them by insensible 

 gradation. Sowerby states his species to be " transversely oblong, with an angular 

 depression in the middle; costsc few, broad, decussated at their upper part, compressed 

 upon the deflected front, each side furnished with two or three spines and a small tube." 

 This description will suit typical specimens, such as the one the author had at the time 



