scnrciiERT.] DEVELOPMENT OF THE NEOTREMATA. 79 



the cause for the thinuess of the shell aiul the lou<?, narrow, attenuated 

 form of its valves. 



The ontogeny of Obolella and Linuuhi shows that one brancli devel- 

 oped directly from the Paterinida'. to Obolida' and Trimerellidie, while 

 another branch began in the Obolida*. The derived branch continued 

 to diverge by changing the thick round shells of the radical stock into 

 thin spatnlate or elongate sulxjuadrate valves, first in the Lingulellidie 

 and culminating in the Lingulida\ The latter family then gave rise to 

 Lingulasmatida^, which, in accordance with the law of morphologic 

 equivalents, devel()])ed some of the internal diagnostic characters of the 

 terminal family of the first phylnm in the phitform of the Trimerellidie. 



Hall and Clarke refer the genera of Liugulasmatidie to Trimerellidie, 

 and thus the latter family, as understood by them, embraces two stocks 

 having widely separated origins. This is peculiar, since thej' clearly 

 understand the independent origin of these 'stocks, as will be seen by 

 the following quotation, but more particularly by their diagram.' 



There is uo single feature in the entire group of the edentulous brachiopods so 

 striking as the great platforms in Trimerella and its allies, and it is rarely that so 

 beautiful and well established an illustration of the attainment of such a remark- 

 able resultant along two distinct lines of development can be presented. 



The writer holds that a natural family can have but one stock, a stock 

 can have but one origin. 



Nonfunctional articular processes are developed in this order in a 

 number of genera and at various times. Such are slightly developed 

 in Trimerella and Monomorella, and more strongly in Tomasina, Bar- 

 roisella, and Spondylobolus. In the Keotremata, articulation is also 

 approached in Trematobolus, and in Crania a false hinge is sometimes 

 developed in Ordovician species. A cardinal process so characteristic 

 of the Protremata and Telotremata is faintly developed in Neobolus, 

 Lakmiua, and Trimerella of the A.tremata. 



NEOTREMATA. 



The order Neotremata begins in the Lower Cambrian, and is repre- 

 sented by 156 species, or over 8 per cent of the brachiopods of the 

 American Paleozoic. It has considerably fewer species than the Atre- 

 mata, and exhibits a lack of specific differentiation, such as form and 

 surface ornamentation. This probably is largely due to the fact that 

 the pedicle is very short, or even obsolete, in this order, and that the 

 pedicle foramen is subcentral, producing in the Trematida? and Cra- 

 niidie more or less of a parasitic growth, while in the families Discinidie 

 and Acrotretida' the great majority of species are circular or oval, with 

 more or less cone-shaped shells. 



As in the Atremata, great tenacity of life is also manifested in this 

 order, since its two essential families, Discinida- and Craniida', have 

 representatives throughout all time since the Ordovician system. 



' Palieontology of New York, Vol. VIII, Tart I, 1892, p. 165. 



