84 SYNOPSIS OF AMERICAN FOSSIL 15RACHI0P0DA. [dull. 87. 



restricted to, the posterior region. The functions of the spines are to 

 hold the animal to its place of habitation, for tliere is no apparent 

 pedicle opening" in these shells when mature. In others of the same 

 family the ventral apex is cemented to extraneous objects (Stropha- 

 losia), and in still others the spines clasp the object of support when 

 small {Strophalosiagoldfiissi and Etheridgina). In the Strophomenidae 

 the older species all seem to have functional pedicles throughout life, 

 but in the Devonian, forms occur in which the apex is cemented to 

 foreign objects (Lepta^nisca). Some of the Middle and Upper Devo 

 nian Stropheodoutas show no trace of a pedicle opening when adult. 

 In the Carboniferous cementation is far more common, and occurs in 

 Derbya and Streptorhynchus; and when taken in connection with 

 Strophalosia, Chonostrophia, Anlosteges, and Eichthofenia, it is seen 

 that nearly all the contemporaneous species of this order have devel- 

 oped other methods for fixation than the normal one. In Eichthofenia 

 calcareous cementation is complete, and the modifications resulting 

 therefrom have so changed the shell that the lower or fixed valve is 

 ver}^ suggestive of a cyathophylloid coral, not only in form but even 

 in shell structure. 



The chief cause for atrophy of the pedicle lies not only in the fact 

 that this organ, in all long-hinged brachiopods, is short, but more par- 

 ticularly in the fact that throughout this order, and in the Acrotretacea 

 of the jSTeotremata, the young shells always have the pedicle completely 

 surrounded by shell, and thus to a great extent limit its growth. Even 

 among the Orthidse, where the species geologically older often have 

 thick pedicles, which is indicated by the large open delthyrium, they 

 gradually diminish in size throughout the Paleozoic. In the Stropho- 

 menidiB the pedicle is never a thick organ, and shortly after this 

 family gives rise to the Productidee, in Chonetes, the first appearance 

 of cementation takes place. This mode of attachment constantly 

 increases in the different phyla to the end of the family histories. In 

 the Productidae the early inheritance of a weak pedicle soon leads to 

 its complete loss by the additional fixation developed. This additional 

 fixation has its first appearance in the cardinal spines of Chonetes, 

 which are periodically developed by mantle extensions. The degen- 

 eracy of the pedicle, once well established, is inherited at earlier and 

 earlier periods by acceleration. The spines become more numerous, 

 and are finally developed over the entire ventral valve. In the dorsal 

 valve, the spines are never so long as in the ventral valve, and often 

 are not developed at all, but are replaced by numerous concentric over- 

 lapping lamellse. As the spines begin to develop more numerously and 

 longer, the ventral valve attains more convexity, with a strongly 

 incurved beak and the complete loss of a pedicle opening. Productus, 

 therefore, does not stand erect on the cardinal areas, as in Chonetes, 

 but lies on the ventral shell, anchored by the numerous spines. The 

 spines are of the same nature as the shells, and never flexible. When 



