BRACHIOPODA. 



301 



FlO. 228. 



Watdheimial {Cryptacanthia) compacta, White and St. John. 



A copy of the original flgaro. 



. (White and St. John.) 



the Upper Coal Measures of Madison county, Iowa, where it is said to be 

 associated with the Terebratula millipundata, Hall {=Dielasma bovidens, Martin). 

 The original figures showing the outline of the exterior are here reproduced. 

 Of the internal structure the authors say that " the loop seems to be essen- 

 tially like that of Waldheimia in 

 form, but the crura of the loop ap- 

 pear to be joined, forming with the 

 hinge-plate a foramen of moderate 

 size ; and the loop-band is armed 

 with numerous spines which point 

 outward towards the shell in all di- 

 rections." 



This shell appears to be very rare, and we have had no opportunity of 

 examining specimens. Attention, however, may be directed to a somewhat 

 similar form of brachidium from the chert beds of the Burlington lime- 

 stone, at Burlington, Iowa, belonging to a species whose identity is not fully 

 established. This structure is represented in the accompanying figure. From 

 a well-developed, elevated and tripar- 

 tite hinge-plate, bearing a slight bi- 

 lobed cardinal process at its apex, 

 arises a very short brachidium of the 

 type of DiKLASMA or Cban.«;na. The 

 outer margins of both descending la- 

 mellae and the short ascending lamellae 

 are bordered with numerous short spin- 

 ules. Furthermore, there appears to 

 be a solid longitudinal band passing 

 from the hinge-plate to the posterior 

 curve of the ascending lamellae. This 

 curious character is not a septum, as the entire apparatus is elevated from 

 the bottom of the valve ; but it may prove to be wholly casual, and a result of 

 an interlocking of the minute quartz crystals with which the brachidium is 



Fio. 226. A fimbriated DIELASHA-Iike brachidium from 

 the chert of the Burlington limestone. 



The median dotted lines indicate'the position of the longi- 

 tudinal band described as probably casnal in origin. 

 The oatline of the valve is wholly constructive. 



