150 PROCEEDINGS OF THE NATIONAL MUSEUM. voi. xxx. 



more i)romin('iit smd commonl}' overlapping the rij^ht or receiving its 

 edge in a shallow groove. 



Type of genus. — Paraparchites humerostus^ new species. 



This genus is established for the reception of the majority of the 

 Carboniferous and Devonian ostracoda that hitherto have been 

 referred to the genus Leperdltia. The writers, however, are satisfied 

 th'cit the genetic relations of these species are not with the Ordovician 

 and Silurian t3^pes of Leperdithi^ but rather with the group of species 

 for which Jones proposed the name Aparchites. True species of 

 LeperdHla always attain a much greater size and their tests have a 

 characteristically black color that is never present in the group of 

 species for which the name Paraparchites is here proposed. The lat- 

 ter are further distinguished from Leperdittd by the character of the 

 ventral overlap of the valves, which is not simple ))ut effected by 

 means of a groove in the edge of the right valve into which the 

 beveled edge of the left valve is received. The relation of the dorsal 

 edges of the valves is also different in the two groups of species, the 

 edges meeting evenly in Lepefrditia while in Paraparchites the back of 

 the left valve commonly projects more or less beyond that of the right 

 valve, and in most cases contains a groove just over the straight hinge 

 line into which the edge of the right valve is inserted. 



As expressed above and indicated by the proposed name, Parapar- 

 chites is regarded as closely related to and probably derived from 

 Aparchites. In the latter, however, the ventral edges of the valves 

 meet without apprecial)le, or, at any rate, constant overlap, and it is 

 this difference that is chiefl}' relied on in distinguishing the two 

 genera. Otherwise the general aspect of the carapace is very similar 

 in th(^ two groups of species, the shape and size being about the same, 

 while the dorsal inequalit}" of the valves is at least sinuilated in certain 

 Ordovician species of Aparchites (e. g. , A. elliptica Ulrich). 



Paraparchites is doubtless closely related also to LeperditvUa^ an 

 Ordovician genus, the principal difference now recognized being that 

 the ventral overlap is reversed in the two genera, the right valve over- 

 lapping in the fcn'mer and the left in the latter. The inter-relations 

 of these two genera and Aparchites are intimate, while their alliances 

 with other types of ostracoda are such as to indicate a distinct family 

 with characteristics that in a considerable degree at least are interme- 

 diate between those of the Leperditiidjv and the Beyrichiida>. Like 

 the latter family, the Leperditellidje, as the new family ma}' be called, 

 were probal)ly derived from some early Ordovician member or mem- 

 bers of the Leperditiida', but the general or average expression of the J 

 new famil}' is more like that of the simple types 6f the Beyrichiidse. 

 In the opinion of the writers, further, the peculiar late Paleozoic to 

 recent germs ( 'ythcretla was derived from Parajxirchitrs or some 

 related genus, and hence from the Leperditellida?. 



