PRODUCTUS. L48 



" crassus." P. auritus of Phillips is another undoubted synonym, while P. Edelburgensis 

 of the same author represents those examples of P. giganteus in which the valves are more 

 coarsely striated, with interspaces of almost equal or greater width, and of which a figure 

 will be found in PI. XL, fig. 2, of the present work. The striatum is, however, sometimes 

 very variable and irregular, even on the surface of a same specimen, and I have at present 

 before me a large example in which the stria? are small, regular, and contiguous for about 

 one inch and a half's distance from the extremity of the beak, then conies a band of 

 about one inch and a quarter in breadth, wherein the ribs become suddenly reduced to 

 nearly half their original number, from many having become obliterated, and thus 

 having left interspaces of irregular width between the remaining stria? ; again, for the last 

 two inches, the stria? become suddenly smaller, twice as numerous, irregularly twisted, 

 unequal in their respective widths, and assuming every kind of modification until they 

 reach the margin. In this example, and in many similar ones, we have therefore com- 

 bined the striation of both the typical P. giganteus and its modification Edelburgensis. 

 The term, P. maxima, was given by M'Coy to that modification of P. giganteus in which 

 the valves are uniformly convex and concave, without longitudinal furrows, while the so- 

 termed P. personatus was established on what is believed by some to be the internal cast 

 of a circular example of P. giganteus, but of which I am not yet perfectly satisfied. We 

 now come to another form, which has by some been considered a synonym, by others a 

 variety, and by many a separate species, viz., P. latissimus, Sow., and I confess that it is 

 not easy to satisfactorily determine which of the interpretations comes nearest the truth. 

 It has, however, appeared to me that if P. latissimus is not a distinct species, it is certainly 

 a well-marked variety, and had better, at least for the present, be separately described. 

 Prod. Scoficus, Sow., and P. pugilis, Phillips, have been classed by Professor de Koninck 

 among the synonyms of P. giganteus ; but this is a mistake, for both those shells, of which 

 I have been able to study the original type, are synonyms of Prod, semireticulatus, as 

 will be hereafter showm. 



In the young state P. giganteus varies almost as much as it does in the adult ; it is 

 at times very slightly convex, while the number of stria? are also far less numerous, these 

 last increasing in number as the shell becomes older, by the means of interstriation or 

 bifurcation. A very great disproportion in the respective thickness of the valves is also 

 usually observable, that of the ventral one being in certain examples five or six times 

 greater than that of the dorsal valve. The spines also were far more numerous in certain 

 specimens than in others, and in some specimens a row of short ones projected from close 

 to the cardinal edge of the ventral valve, but never as represented by Von Buch in PI. I, 

 fig. 1, of his monograph, 1 such a restoration is founded on a supposition which no example 

 I have seen has ever warranted, but they occur sometimes as represented in his fig. 3. 



Loc. Productus giganteus is common in the English grey lower carboniferous limestone 



1 *Ueber Productus oder Leptaena Gelesen in der Akademie der Wissenschaften,' 1841. 



