2 Prof. W. King on Spirifer cuspidatus. 



which he has '^ transferred" to the so-called ^^ isomorph " are 

 neither ^^generically" nor specifically " diiFerentiated " from 

 the species under consideration, that, histologically and in- 

 ternally, the perforated and canaliferous specimens are iden- 

 tical with those stated to be " imperforate " and without the 

 septum. 



External Gonformation. 



Few Palliobranchs have so singular an appearance as Spi- 

 rifer cuspidatus. While its spiriferal valve deviates in no 

 marked degree from ordinary species, being semielliptical and 

 flatly convex, its opposite one is characterized by an erect 

 elevated umbone and an enormously developed area, which 

 give quite a pyramidal form to the shell. 



Instead of being incurved, as is usual, tlie umbone displays 

 more tendency to the opposite character, or to become twisted, 

 like that of Btreptorliynchus. The area varies in outline be- 

 tween an equilateral and an acute isosceles triangle, and, as 

 in most Spirifers, it is both transversely and longitudinally 

 marked with faint lines. The deltoid fissure is well exhibited; 

 but whether it was closed in all its length with a deltidium, 

 as is the case in the allied 8p. distansj Sowerby, or merely in 

 its lower part, is a point which I am unable to determine. I 

 have represented in PL II. fig. 1 a specimen of Sp. cuspidatus 

 presented to the Geological Museum of Queen's College, 

 Galway, by my very respected colleague. Dr. M^Coy, Professor 

 of Materia Medica, which shows, what is rarely exhibited, the 

 deltoid fissure near its base covered with a number of arching 

 lamellae; but nothing of the kind occurs higher up : so there 

 is just as much reason for concluding that the upper part has 

 been destroyed as that it never existed. If, as appears to be 

 the case, the semicircular space below the arching lamellae has 

 served as a foramen or opening for the pedicle, the circum- 

 stance would afford some ground in favour of the first con- 

 clusion*, and consequently of the species being furnished with 

 a deltidium like that of 8p. distans'f. 



Both valves are marked with numerous fine ribs, which, 

 however, occasionally become obsolete ; and this is generally 

 the case on the median folds. 



* I would suggest to American palseontologists who have an opportu- 

 nity of collecting casts of apparently this species, abundant in the Car- 

 boniferous sandstone in the State of Ohio, to examine impressions of the 

 area, when, no doubt, they will be able to determine whether the deltoid 

 fissure is partially or completely closed. 



t Several of Mr. Davidson's figures represent specimens of this species 

 with the deltoid fissure completely closed. (See Mon. Brit. Carb. Brach. 

 ph 8, and Geol. Mag. July 1867, pi. 14. figs. 7 & 9.) 



