324 PALMONTOLOGY OF NEW YORK. 



frequently scattered irregularly over the surftice, generally strongest and dis- 

 posed with greatest regularity upon the cardinal extremities, and sometimes oc- 

 curring only in this region. They are hollow and appear to have communicated 

 with the interior cavity of the shell. On the interior of the valve is a narrow 

 median ridge, separating the two dendritic impressions of the adductor muscles; 

 outside and in front of these are two broadly Habellate, longitudinally striated 

 scars of the cai'dinal muscles. In the pallial region are sometimes found traces 

 of spiral cavities, which were occupied by the tleshy arms.* 



The brachial valve is operculiform, more or less concave or .almost flat over 

 the visceral area. Cardinal area, sockets and crural plates absent or rudi- 

 mentary ; cardinal process strong, curved or erect, extending far above the 

 hinge-line ; its inner face is divided into two lobes by a longitudinal furrow, 

 and each of these parts is deeply divided at its extremity, giving the process 

 in this aspect a quadrilobed appearance. As viewed from the posterior or outer 

 face it is strongly trilobed, the inner members of the lateral lobes coalescing to 

 form a very prominent apophysis. The process is continued over the interior 

 of the shell as a longitudinal septum, dividing the impressions of the adductor 

 muscles. The latter are strongly dendritic and rarely divisible into anterior 

 and posterior elements. The brachial ridgesf take their origin from near the 

 post-lateral margins and nearly enclose a sub-circular, smooth or granulose 

 area. The internal surface of this valve is strongly postulose, and in the 

 pallial region frequently spinous. 



* See Davidson, British Cai-buuilerous Brachiniiotla, j>l. xxxvii, tiff. 1. IStJl. 



t Waagen says (Productus-limestone Fossils, p. 611): "A passage in Professor Nedmayr's paper 

 [Neues Jahrbuch fiir Mineralogie, 1883, vol. ii, p. 27], which is of very great impoitance, I must quote here 

 more in detail. He says, a chief olijection of Davidson's against the opinion that these ridges form a part 

 of the brachial apparatus is the existence of spiral impressions which are to be found in the ventral valve 

 of some specimens of Pkoductus, and which beyond any doubt are impressions of the spiially enrolled ai'ms 

 of the animal. Now, as tliese impressions show not the slightest accordance with the brachial ridges [reni- 

 form impressions], Mr. David.son concludes that these latter cannot be taken as belonging to the brachial ap- 

 paratus. 'I cannot concur,' says Professor Necmayh, 'in this argument. The greatest number of the now 

 living Brachiopods have arms showing a double curve ; and if such were, as is probable, present in Pro- 

 DUGTBS, these features (the ridges in the one and the spiral impressions in the other vahe) are in no way 

 difficult to explain ; on the contrary they indicate very accurately the direction and the manner in which the 

 arms extended in Productus. They run first along the descending, then along the reascending branch of 

 the ridges, were then bent back over the descending branch, and curled in a spiral coil, which caused the 

 impression in the ventral valve. Thus, in their general shape, these arms very nearly agree with those 

 occurring in Tbrbbratdla and Waldhbimia, though in proportion and direction of the different parts certain 

 diffei-ences exist.' This deduction is of very great systematic importance." 



