324 PALEONTOLOGY OF NEW YORK. 



frequently scattered irregularly over the surface, 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 flabellate, longitudinally striated 

 scars of the cardinal muscles. In the pallial region are sometimes found traces 

 of spiral cavities, which were occupied by the fleshy 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 Carbunil'eious Brachiopoda, pi. xxxvil, tig. I. ISbl. 



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

 [Neues Jahrbuch fiii- Mineralogie, 1883, vol. ii, p. 27], -whicli is of very gi'eat importance, I must quote here 

 nioi-e in detail. He says, a chief objection of Davidson's against the opinion that these I'idges 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 Pkoddctds, and which beyond any doubt .are impressions of the spirally enrolled arms 

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

 form impressions]. Mi'. Davidson concludes that these latter cannot be taken as belonging to the brachial ap- 

 paratus. 'I cannot concui',' says Professor Nbdmatr, '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 Pbo- 

 DUCTDS, these features (the ridges in the one and the spiral impressions in the other vah e) are in no way 

 difficult to explain ; on the contrai-y they indicate very accurately the direction and the manner in which the 

 arms extended in Produotds. They I'un 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 Terebratula and Waldhbimia, though in proportion and direction of the different parts certain 

 differences exist.' This deduction is of very great systematic importance." 



