334 CAMBRIAN BRACHIOPODA. 



Meek's original reference to Micromitra [1873, p. 479] is as follows: 



It is quite probable that when specimens showing clearly all the characters of this shell can be examined it will 

 be found to belong to an undefined genus, either of the Brachiopoda or some other group. In this case I would propose 

 for this genus the name Micromitra. 



The type specimen labeled by Meek in 1873 as IpJiidea (Micromitra) sculptilis is in the col- 

 lections of the United States National Museum (Catalogue No. 7864). The label is in Meek's 

 handwriting and firmly attached to the specimen of rock containing the shell. 



The description of the shell referred to Iphidea (ff) sculptilis Meek [1873, p. 479] is that of 

 the ventral valve. Wliile no generic description is given and the specific description is incom- 

 plete, we are necessitated by the present rules of nomenclature to accept the name Micromitra, 

 since IpJiidea, as proposed by Billings [1872b, p. 477], was preoccupied by Baly in 1865. 



When away, engaged in field work, I accidentally discovered that the genus Iphidea was 

 first used by Baly in 1865. I then put the name Iphidella in some manuscript notes and by 

 oversight this name was published [Walcott, 1905a, p. 304]. Schuchert [1905, p. 329] called 

 attention to its being a synonym of Micromitra and Paterina. This is shown in my synonymy 

 of the genus IpJiidea [1897b, p. 707]. I now use IpJiidella as a subgenus of Micromitra. 



Billings's description of the genus IpJiidea and that of the type species were combined. At 

 the time of my study of Kutorgina and IpJiidea [Walcott, 1886b, p. 100] I did not agree with 

 Billings in his reference of "Obolus lahradoricus" to IpJiidea [Billings, 1874, p. 76]. Since that 

 time I have collected more material representing this group of shells, and from its study have 

 come to the conclusion that Billings was correct in referring "0. lahradoricus" to his genus 

 IpJiidea. The ventral valve of "0. lahradoricus" has a narrow false area of the same type as 

 MicroTTiitra {Paterina) hella (Billings), and the characteristic pseudodeltidium is clearly shown 

 in a section, and it is known to occur in Micromitra sculptilis (Meek), Micromitra {IpJiidella) 

 ornatella (Linnarsson) , and M. (/.) pannula (White). The extreme development of the false 

 area and pseudodeltidium is found in M. {P.) superha (Walcott), from the Middle Cambrian 

 "Tonto" sandstone of the Grand Canyon of the Colorado. In this form the ventral valve is 

 broadly conical, and the large pseudodeltidium projects backward at an angle equal to the slope 

 from the apex to the front. In Micromitra {Paterina) hella the false area slopes more abruptly 

 downward and in Micromitra {IpJiidella) ornatella it is nearly vertical, the pseudodeltidium being 

 much shorter and projecting but a short distance beyond the area. The slope of the area of M. (/.) 

 ornatella is essentially the same as that of Micromitra {Paterina) lahradorica swantonensis (Wal- 

 cott), which is the type of Beecher's genus Paterina. (See p. 344.) In some specimens of the 

 latter species the beak projects so that the slope of the area carries it forward to a considerable 

 distance under the beak. This is also true of Micromitra {IpJiidella) pannula. 



The presence of an apical foramen in Micromitra (Paterina) hella and Micromitra {IpJiidella) 

 ornatella would separate those species from the Paterinidse, but from a careful study of all the 

 evidence attainable I am led to question the presence of a true apical foramen in either species. 

 Unless there are other characters than those shown by the false area and pseudodeltidium and 

 the angle at which they slope, it will be impracticable to generically separate Micromitra {Pater- 

 ina) hella and M. (P.) lahradorica and the other species mentioned. 



In his original description, Billings [1872b, p. 478] says: 



In the specimen above figured there is an aperture in the beak, but in another there is no appsarancs whatever 

 of a perforation. 



In a fine series of Micromitra {Paterina) hella from the Lower Cambrian, south of Emigs- 

 ville, York County, Pennsylvania, the characteristics of the genus and species are strikingly 

 well shown. In none of the specimens is there in the ventral valve an indication of an apical 

 pedicle opening. The dorsal valve is slightly elevated, and in the half-dozen well-preserved 

 specimens no trace has been observed of any false area or pseudodeltidium; but in Micromitra 

 {IpJiidella) pannula the false area is even more clearly defined than in the ventral valve, and 

 the pseudodeltidium is present as a depressed concave covering of more than one-half of the 

 triangular space inside the narrow area on each side. The area on the dorsal valve has also 

 been observed in M. (/.) ornatella (Linnarsson) and Micromitra {Paterina) lahradorica (Billings). 



