19t) l>r. A. Vau-^liaii on IScuiinula. 



{b) Radial. There is no clear indication, either on the 

 cast or on the remnant of the test, of the impressed ^labii- 

 striation which characterizes the Athyrids provided \vith 

 frinj^od or ribbed flounces {CIciothyris and Actinoconchus). 



[On tlie same tablet M-iti) the tyi)e specimen of Ter. pent- 

 aeolra in the Ciilbertson Collection arc nine other specimens. 

 Ei^ht of these have well-preserved double-valves, and can be 

 assigned with certainty to an Athyrid provided with fringed 

 or ribbed flounces, by reason of the radial impressed ornament 

 and the low beak. It was probably on the evidence of these 

 specimens that Phillips accredited a minute perforation to his 

 species Tti'. peutaedra. These specimens differ completely 

 from the type specimen in form, beak, ornament, and nature 

 of fold. 



Tlie remaining specimen on the tablet (a cast) approaches 

 more closely to the type specimen both in form and beak, 

 but differs in exhibiting conspicuous glabristriation. Where 

 broken it exhibits part of a spire.] 



Discrimination of the Genotype of Semi'nida from other 

 Genera. 



The holotype of Terehratula pentaedra, Phillips, differs 

 from the following genera in the characters subjoined. 



From Camarophoria [genotype : JWebratu^a Schlotheimi, 

 von Buch] in the fact that the dental j)lates do not unite, 

 absence of mesial septum, absence of angular plaits, low mesial 

 fold, &c. 



From 2Jartinia [genotype : Spirifer glaher (Martin)] in 

 presence of dental plates, absence of area, excavated mesial 

 fold, &c. 



From Dielasma [genotype : Terehratula elongatus (Schlo- 

 theini)] in impunctate test and the nature of fold. 



From the Athyrids with fringed or ribbed flounces \_Cleio- 

 thyris (King), genotyj)e : Afrypa pectinifera, J. de i). Sow.] 

 in the outline, the nature of the fold, the absence of glabri- 

 striation, and the produced beak. 



From Actinoconchus [genotype: Actinoconchus paradoxus, 

 M'Coy (which is united with Spirifer planosu/catuSf Phill., 

 by Davidson)] in the deflection of tlio valve-intersection and 

 the presence of a mesial told, the absence of a mesial septum 

 in the pedicle-valve, and the absence of glabristriation. 



On the other hand, the type specimen of Seminula agrees 

 in all its generic characters with Spirifer ambiguus, ^ow., 

 from which it only differs specifically in the lower fold and 

 more flattened shell [as was pointed out by Davidson (Pal. 



