283 



than the lateral. Surface of the test unknown, that of the cast marked 

 by large, transverse rib-like plications, which are moderately prominent 

 on each of the sides, but obsolete on the periphery or venter, — and by very 

 small, acute, thread-like spiral ridges. The transverse plications are 

 rather distant, slightly flexuous and somewhat sigmoidal on each side of the 

 outer volution, where they are separated by wide and shallowly concave 

 depressions. The small spiral ridges are numerous, comparatively close 

 together, though not very regularly disposed, and in one specimen, at least, 

 rather larger and more prominent on the periphery of the outer volution 

 than on its sides. Sutures of the septa concavely arched on both of the 

 sides, where each suture intersects one, or rarely two, of the transverse 

 plications. Shape and position of the siphuncle unknown. ' 



" The. first specimen of this shell that the writer had seen was given to 

 the late Chief Justice Wallbridge by a quarryman at Stonewall and pre- 

 sented to the Museum of the Survey by Prof. E. J. Chapman in 1895. 

 ' The exact locality from which this specimen was obtained was for a long 

 time doubtful, but there is now every reason for believing that it came 

 from the quarries at Stonewall. At any rate, in the fall of 1897, two 

 specimens, which are known to have been collected at Stonewall, were 

 presented to the Mussum, oae by Mr. John Gunn, and the other by Mr. 

 W. H. Robson. At tlie sa v,e time, also, Mr. Tyrrell obtained a charac- 

 teristic fragment of a specimen of this species, in situ, at the Stonewall 

 quarries. By far the most perfect of the specimens yet received is the 

 one presented by Mr. Gunn, and figured on Plate 41. It has two entire 

 volutions preserved, which are gyroceran rather than nautilian in their 

 mode of coiling, but very slightly asymmetrical. The inner volution is 

 openly coiled, the apex or initial point being widely eccentric, and 

 there is a large central perforation about an inch and a quarter in 

 diameter. 



" These specimens seem to indicate a previously undescribed species, 

 which is here referred provisionally to Trochoceras rather than to 

 Lituites, until the shape and relative position of its siphuncle be ascer- 

 tained, when it may have to be transferred to Plectoceras, Peismoceras or 

 Discoceras. It difiers from Lituites Biakmoreanus, Whitfield (from the 

 Niagara limestone of Indiana) which Hyatt says is a Plectoceras, in its 

 more openly coiled inner volution, in its broadly elliptical and not sub- 

 quadrate cross section, and in its closer transverse plications, which are 

 quite obsolete on the periphery. Professor Whitfield, who has kindly 

 compared two of the best specimens from Stonewall with the types of his 

 species, thinks that the two forms are quite distinct. 



