BRACmOPODA. 165 



As suggested above, certain linguloid characters, in which form and the 

 structure of the pedicle-passage are paramount, have departed toward Lingula 

 by the way of Lingulella. Another combination of linguloid features, in 

 which the muscular scars are of primary importance, but the form still obolel- 

 loid, is represented by the genus Obolus. Here the muscular bands have 

 become specialized to such a degree that in the pedicle-valve they approach 

 closely to Lingula, while in the other they retain more distinctly the obolelloid 

 character ; moreover, the subcircular form and the persistence of the pedicle- 

 groove on both valves are features of Obolella. 



Obolus, therefore, is a more specialized form than Obolella and less so than 

 Lingula. The aberrant Neobolus appears to hold intermediate structural rela- 

 tions to both Obolus and Obolella, except in the existence of a strong cardinal 

 process in the brachial valve, a feature indicating progress in this line of 

 derivation, toward characters of the articulate brachiopods. 



The typical combination of obolelloid characters is continued, without essen- 

 tial variation, into the genera Leptobolus and Schmidtia, while Paterula, 

 whose structure demonstrates its close alliance with Leptobolus, presents a new 

 feature of great importance in its minute, incised, marginal pedicle-aperture. 

 In ScHizoBOLUS we find the same features superinduced upon the substantially 

 unaltered muscular scars of Obolella. 



While discussing the origin and development of the platform in the inarticu- 

 late brachiopoda, we have referred to the fact, that Obolus, in having its 

 muscular scars excavated, as in Lingula, and not elevated on a central thicken- 

 ing, as in the other forms constituting the linguloid line of development toward 

 Trimerella, holds the same relation to the genus Elkania, as does Lingula to 

 Lingulops. Further, that Elkania represents, by virtue of this variation, an 

 important progress in the development of trimerelloid characters along the 

 obolelloid line, connecting with Trimerella by way of Dinobolus. There is no 

 single feature in the entire group of the edentulous brachiopods so striking as 

 the great platform in Trimerella and its allies, and it is rarely that so beautiful 

 and well-established an illustration of the attainment of such a remarkable re- 

 sultant along two distinct lines of development can be presented. 



