286 Raymond — Common .Devonian Brachiopods. 



they are bounded by a low ridge in front, while in S. per plana 

 the anterior margin is more indefinite. 



The interior of the dorsal valve of P. iowaensis should 

 also be compared with that of S. profunda Hall, from the 

 Niagara.* In that species the form of the scars is almost 

 exactly the same as in the Hamilton species, and in front of 

 the scars there are two short curved ridges and a prolongation 

 of the median septum. This species has been put in the 

 division Brachyprion by Hall and Clarke. 



Thus there are examples of four of Hall and Clarke's sub- 

 divisions, — Brachyprion, Leptostrophia, Pholidostrophia, and 

 Stropheodonta {S. demissa type), which agree in internal 

 structure, but have great variation in external ornamentation. 

 These facts would seem to indicate that the name Pholido- 

 strophia should be given the same taxonomic value as the 

 names Brachyprion and Leptostrophia, instead of being raised 

 to generic rank. 



Orthothetes chemungensis Hall. 



Orthothetes chemungensis var. pectinacea Hall. 



(Plate XV, Eow 1.) 



Pal. N. Y., iv, 1867, p. 67, pi. 10, fig. 6. 



Orthothetes chemungensis var. arctistriatus Hall. 



(Plate XV, Eow 2.) 

 Pal. N. Y., iv, 1867, p. 71, pi. 9, figs. 1-12. 



The specimens of Orthothetes in the present collection rep- 

 resent the two varieties pectinacea and arctistriatus of Hall. 

 Both develop in the same manner, the only difference being in 

 the time of appearance of new striae. In the adult these two 

 forms can be separated only under the most favorable circum- 

 stances, yet the younger specimens are quite distinct. The 

 variety pectinacea has from 15 to 19 strong elevated striae, 

 between which are lower interspaces containing from 1 to 3 

 striae. In the variety arctistriatus the striae are so crowded 

 that this alternating appearance is not obtained. 



Smallest Shell. — The smallest shell which retains both 

 valves is -73 mm long and l*l mm wide, with a hinge width of 

 l ram . Both valves are convex, and the cardinal area is high. 

 The delthyrium is almost completely closed by a strong, con- 

 vex deltidium which is slightly prolonged at the apex, forming 

 an exsert pedicle tube. On this specimen there are 13 striae 

 on the dorsal and 14 on the ventral valve. At the beaks can 

 be seen the outline of the nepionic shell, which is almost 



* Loc. cit. 



