3 2 '2 PROCEEDlNas OF THE NATIONAL MUSEUM. voi. xxvni. 



forward and outward from the apex, a little inside of the grooves of 

 the main vascular ti'unks; this structure is apparently the result of the 

 union of the area with the bottom of the shell, so as to bring, as the 

 shell grew, the path of advance of the pedicle groove, main vascular 

 sinuses, and lateral muscle scars all on one surface instead of on the 

 area and the shell beneath it, as in OJxthis. 



The muscle scars are arranged as in (Jhohts. The transmedian and 

 anterior laterals occur well out toward the margin, and the space 

 inclosing the central scars, middle and outside laterals, is in the central 

 area, on the front of the slope of the thickened posterior portion of 

 the valve; the points of attachment of the individual muscles can not 

 be distinguished. In the doi'sal valve the central and anterior lateral 

 scars are clearly shown in several specimens. The transmedian and 

 outside laterals are situated just outside the main vascular sinus. Our 

 knowledge of the vascular markings is limited to the main vascular 

 sinuses, except in one ventral A^alve where the inner branches have been 

 preserved. In l)oth valves the main trunk rises near the apex and its 

 path is outlined across the reversed area. 



The preceding description differs materially from that of Messrs. 

 Ford and Hall and Clarke. I tind the muscle scars as described above, 

 and am compelled to consider them as indicating the same muscles as 

 in Ohol )is. That the genus is an advance on Oholus in the evolution 

 of the inarticulate brachiopods, I quite agree with Hall and Clarke; 

 also that it is a stage in the transition from OhoJus to TrlriiereUa and 

 its allies. The stage, however, is not far along, as nothing is seen of 

 the platform in advance of the area, and the area is merged into the 

 body of the shell. Ell'iohla is an (>h<)lu><\\\\\\ the cardinal areas within 

 the plane of the margins of the valves. In the type species, ^i^. desid- 

 eratd^ the area of the ventral valve is entirely within the valve, while 

 that of the dorsal valve has been nearly obliterated in the process of 

 change from an open backward-facing area to an inclosed forward- 

 facing area. A compaiison of the interiors of Oholus {L.) codatus 

 and (Jholvs apolUnis with those of ElJainla desiderata and Elhanta, 

 hdhda illustrates that little change is necessar}^ to convert the exterior 

 cardinal areas of Oholus into the inclosed reversed areas of Elkania. 



As the beaks of EJkania are marginal, the pedicle passed out 

 though an opening made by the gaping of the valves. 



The four kiiown species of the genus are the tvpe species, EJkanla 

 desiderata^ E. ida, E. amhix/ua, in which the shell is very thick, and 

 E. helhdu, a minute shell in which the form and tendency is towards 

 LhigidelJa rather than the thick oval forms of Oholus. 



hingidasina Ulrich, has an inclosed cardinal area, and is a more 

 advanced stage than Elkania in the transition from Oholus ?indi its sub- 

 genera to the true Trimerelloid forms." 



«See Pill. New York, VI II, I't. \,\^\^. 24-28, .'W-SS. 



