R. ETHERIDGE, JUX., OX A LOWER-CARBONIFEROTJS PRODUCTUS. 461 



(figs. 13-20, 22, 24), sometimes almost becoming geniculate. In 

 the dorsal valve they are perhaps finer and more numerous than in 

 the ventral valve ; and in the visceral region of the shell the circular 

 concentric character gives place to an almost square concentric form 

 of wrinkle or corrugation (figs. 18, 24). As the shells increased in 

 age the corrugations became broken up in a roughly reticulate manner 

 (figs. 22, 24). In the young state the ventral valve only is partially 

 covered with spines (figs. 13, 14), the dorsal being devoid of them 

 (fig. 19) ; but as growth went on they also appeared on the latter, 

 but apparently without attaining to the same size. The spines are 

 irregularly scattered over the surface of the valves ; those of the ven- 

 tral valve long, thin, tapering (figs. 16, 17), and encircling (fig. 11), 

 and when broken leaving the shell covered with a series of small warts 

 (figs. 13-17). A row of prominent strong spines occurs along and 

 immediately below the hinge-line of the ventral valve (a, figs. 16, 

 17), but in the two figured examples broken off. In a few instances 

 one or more of the spines may be seen pressed down against the sur- 

 face of the ventral valve, as if it had so grown between the shell 

 and the object to which it was attached, without encircling the 

 latter. The umbo of the ventral valve is small, sharp, plain, and 

 slightly incurved over the hinge-line. The visceral region of the 

 same valve is often grooved vertically or indented, the impression of 

 the body to which the individual was attached, such grooving eleva- 

 ting the beak (figs. 13, 14) and obliterating the corrugations on 

 other portions of the valve more than would otherwise be the case. 

 The adductor muscular scars are only preserved distinctly in one 

 specimen. They appear to be elongated vertically, and are appa- 

 rently lobed transversely. 



4. Considerations as to Specific Identity. The question which 

 most prominently presents itself is : — Is this adherent Productus the 

 young of some well-known species, or is it to be regarded as a minute 

 and undescribed form ? Let us examine the evidence that we possess 

 to settle this question. Of the unattached examples fully two thirds 

 are dorsal valves. The predominance of these over the ventral valves 

 would appear to indicate that it was at least an attached species up 

 to that point of its existence represented by the largest of our speci- 

 mens, which are dorsal valves, and which may, I think, be taken as 

 representing maturity, unless very strong evidence to the contrary 

 can be produced. It is only reasonable to suppose that had the 

 Productus at a certain point of its life disunited itself from the 

 Crinoid stems, upon which it had hitherto lived, we should be in 

 possession of relatively as many large, and what I take to be mature, 

 ventral as dorsal valves. But we are not ; for out of a large number 

 of specimens now in the possession of the Geological Survey of Scot- 

 land and Museum of Practical Geology nearly all the largest examples 

 are dorsal valves. 



When Mr. JBennie was fortunate enough to light upon these 

 interesting fossils, I at once submitted characteristic examples to 

 Mr. T. Davidson, F.R.S., who, in his usually kind manner, gave 

 me the benefit of his valued opinion. He pointed out that the 



