PRODUCTUS. 173 



Surface covered with numerous sub-regular, concentric bands or ridges, which increase in 



number and breadth as they recede from the extremity of the beak, but in adult shells 



becoming again closer as they approach the margin ; these bands (in the ventral valve) are 



slightly raised towards their lower margin, and are abruptly separated from each other by 



a narrow, smooth space, after which there exists a tolerably regular row of lengthened 



tubcrcules or slender, shining, tubular spines, and again below these the remaining space is 



filled up by irregularly scattered, but closely packed, smaller spines, all overlapping one 



another, and lying close to the valve. Dorsal valve moderately concave, with a slight 



mesial elevation, and ornamented as in the dorsal one, but the bands are slightly concave. 



In the interior of the ventral valve the adductor or occlusor muscular impressions extend 



much lower down in the shell than do those attributable to the divaricators. In the 



dorsal valve the muscular and reniform impressions differ but slightly from those of other 



Producta. Two specimens have measured — 



Length 28, width 31, greatest depth between valves 12 lines, 

 oo on 1 l 



Obs. This common and very characteristic species appears to have been described and 

 figured for the first time by David Ure, who mentions that " both valves are covered with 

 small spines resembling hair, and so numerous that a largish example contains upwards of 

 ten thousand, and lie so closely together that the surface of the shell is entirely concealed 

 from view," 1 but it is rare to find the specimens in that condition, the valves being usually 

 deprived of their spiny investment. Martin appears, however, to have been the first 

 naturalist who applied to the shell a specific denomination, but he confounded under the 

 same name the P. fimbriates of Sowerby, a closely allied, but easily distinguishable species. 



Productus elegans has been generally considered a synonym or a young condition of the 

 shell under description ; but as I am still uncertain whether it be really so or a distinct 

 species, as believed by M'Coy, it will therefore be preferable to describe it separately, but, 

 perhaps, as a variety of P. pundatus, to which it bears much resemblance in the arrange- 

 ment of its spines. P. pundatus is characterised in all well-shaped examples by a median 

 depression or sinus, but as this commences usually at a short distance from the extremity 

 of the beak it has been supposed, correctly or erroneously, that in the young state the ventral 

 valve may have been convex and without sinus (?). 



Var? elegans, M'Coy. PL XLIV, fig. 15. 



Productus elegans, M'Coy. Synopsis Carb. Foss. Ireland, pi. xviii, fig. 13, 1844; and 

 British Palaeozoic Fossils, p. 460, pi. iii H, fig. 4. 



Shell rather small, longitudinally ovate ; hinge-line a little shorter than the width of 

 the valve. Ventral valve regularly arched and gibbous, without sinus. Surface crossed 



1 'History of Rutherglen and East Kilbride,' pi. xv, fig. 1, 1793. 



