PKOM CTUS. 145 



05s. Much difference of opinion has been expressed relative to the shell under 

 description, and it was not until after much examination and hesitation that I determined 

 to provisionally retain the shells first figured by James Sowerby, in tab. 328 of the 'Min. 

 Conch./ as a variety of P. g ig anteus — a view entertained by Prof, de Koninck, when pub- 

 lishing his monograph in 1847. Prof. M'Coy, describes them as belonging to another 

 and distinct species ; so that the subject may still remain an open question, although I am 

 myself inclined to consider P. hemispharicus as nothing more than a local variety of Pro- 

 ducing giganteus? Mr. E. Wood, who has had occasion to collect in situ some hun- 

 dreds of specimens of this and the typical shape, assures me that the one never occurs in 

 the same bed or zone along with the other; that the bed in which the P. hemispharicus 

 occurs runs for miles along Warfdale in Yorkshire, and that the layer is covered and filled 

 with closely packed specimens of this one fossil, which is also always exactly the same, 

 and much under the true P. giganteus bed. My reasons for supposing it a variety of P. 

 giganteus are based on the following consideration, viz., that I have several times seen large 

 examples of P. giganteus evenly convex, and closely resembling some of the smaller 

 specimens of P. //p/uis/jf/aricus above described, 1 and it is well known that the longitudinal 

 furrows which cover the valves of many examples of Martin's shell are not always present ; 

 that the striation of P. hemispharicus agrees likewise with that of many specimens of P. 

 giganteus, and that the small curved cardinal spines so constantly present in the Warfdale 

 specimens are also observable in many undoubted large examples of Martin's shell ; and, 

 Iastlv, that the interior is smaller in both. I have also had the advantage of being able 

 to study James Sowerby's original specimens of P. fiemisp/iaricus, and found them to agree 

 with those from the gray carboniferous limestone of Warfdale, in Yorkshire. 



Productus latissimus, J. Sowerbg. Plate XXXV, figs. 1 — \. 



Productus latissimus, J. Sow. Min. Conch., pi. 300, Feb., 1822. 



— — Phillips. Geol. of Yorks., vol. ii, pi. viii, fig. 1, 1830'. 



— — De Koninck. Monographic flu genre Productus, pi. ii. lig. 2, 



and pi. iii, fig. 2, 1847. 

 — Dae. Scottish Carh. Brach., pi. ii, figs. 8, 9, 1861. 



Spec. Char. Shell thin, transversely elliptical or spindle-shaped, with a long, straight 

 hinge-line, the breadth of the shell being more than twice the length. Ventral valve 

 very much vaulted and convex, with a slight mesial longitudinal depression, the 

 gibbosity forming in profile more than a semicircle, while the passage from the body of 

 the valve into the lateral expansions is usually so gradual as to become insensible. The 

 small flexuous striae which cover the surface augment by the means of numerous interca- 



1 In his work on * British Palaeozoic Fossils,' Professor M'Coy has considered P. av.rita to be a 

 synonym of P. hemisphcericus ; and I feel convinced, that any one who examines the Gilbertson specimens of 

 the first (now in the British Museum) will class it among the synonyms of P. yiyanteus. 



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