PRODUCTUS. 147 



Productus humerosus, /Soto. PI. XXXVI, figs. 1, 2. 



Productus humekosus, Soiv. Min. Conch., t. 322, January, 1822. 



— tiokkidus, De Koninch. Mon. du genre Productus, 184/ (not of Sow. ?) 



— aculeatus (Schlotheim) , Von Buck. Uber Productus oder Leptacna 



Akademie dcr Wissenschaften, p. 35, 1841. 



Of this Productus internal casts alone have been hitherto found, so that no description 

 of the exterior can be given. The length generally slightly exceeds the breadth, while 

 the hinge-line is usually somewhat shorter than the width of the shell. The ventral 

 valve was gibbous and of great thickness, with perhaps a slight longitudinal depression or 

 sinus? while the dorsal one was concave, light, and thin. The interior details are sharply 

 sculptured upon the internal casts. The ventral valve in the cast is very remarkable on 

 account of two large projecting conical protuberances situated about the middle of the 

 shell, with their extremities directed towards the beak, and which in the enormously 

 thickened shell formed very deep cavities, which no doubt afforded accommodation to the 

 spirally coiled ? oral arms. The muscular impressions form also in the cast a remarkable 

 protuberance, and in the shell itself occupy the rostral or incurved portion under the 

 cavity of the beak. The adductor or occlusor produces two radiating dendritic impressions, 

 longitudinally divided by a narrow ridge, and on either side there is (in the shell) a deep, 

 strongly grooved or striated sub-quadrate impression, which is due to the cardinal or 

 divaricator muscle, the remainder of the inner surface of the valve being covered with 

 rugosities. In the interior of the dorsal valve, the quadruple impressions of the adductor, 

 as well as the reniform impression, do not differ from those of the generality of Producta. 

 The absence of the shell itself renders specific determination uncertain, and the name is 

 consequently only provisionally retained. In their monographs, Baron von Buch and 

 Prof. L. de Koninck have placed P. humerosus among the synonyms of the Permian P. 

 horridus ; and although I would not deny the possibility of this view being correct, still as 

 none of the internal casts of the Permian shell, that have come under my observation, have 

 exhibited those enormously developed and peculiar conical protuberances present in the 

 Carboniferous casts, and as the muscular impressions in the ventral valve differ also some- 

 what in their details, I have preferred (at least provisionally) retaining the denomination 

 under which the Carboniferous Productus is generally known. 



The internal casts of P. humerosus are from the Magnesian Limestone of the Car- 

 boniferous series of Breedon in Leicestershire, and a fine series of specimens may be seen 

 in the Collection of the Geological Society and British Museum. 



