THE FAUNA OF THE ST. JOHN GROUP. 59 



than the true Stenothecœ, and is preserved iu a different attitude in the shales. Stenothecse 

 proper present us with shells which have a tendency to be flattened along the vertical 

 plane, but this species is always found iu the shales compressed horizontally, or parallel 

 to the aperture. An examination of the younger stages of growth of this shell shows a 

 high apex and dorsal line with flattened sides, and a tendency to collapse laterally like the 

 true Stenothecœ. While, therefore, it shows close relations with this genus in its younger 

 stages, the adult is- so different in appearance that we seem warranted in separating it as a 

 swhgonws. 



S^uhgenns.—PARMOPHORELLA. 



Distinguished from Stenothecœ proper by its limpet-like form and broad aperture. It 

 also has the following characters : Apex recurved, muscular impression horse-shoe shaped, 

 elongated, encroaching upon the enclosed space in the anterior part of the shell. 



Stenotheca (Parmophorella) Acadica. (Plate YI. Figs. 10, lOrt, b, and r.) 



Discina Acadica, Hartt. Acad. Geol., 2nd Ed., p. 644. 



Palœacmea (?) Amdica, Walcott. U. S. Geol. Surv., Bull. 10, p. 19, PI. I. Fig. 6. 



This shell was described by the late Professor C. F. Hartt as a Discinn. Subsequently 

 Mr. R. P. Whitfield observed that the shell substance was calcareous, and concluded that 

 it was a gasteropod, allied to Palœacmea or Metoptoma. Mr. C. D. Walcott afterward 

 referred it to the former genus, and subsequently to Dr. Hicks' genus, Stenotheca. This is 

 where the late Mr. Billings would have placed it if one may judge from a remark in his 

 " Palœozoic Fossils," (Vol. II. p. 78.) With this view the author coincides, except that the 

 form so far differs from the true Stenothecœ as to deserve a subgeneric distinction. 



" The following is Professor Hartt's description of the species : — " Shell elliptical in 

 outline, sides more or less straight. Conical, but very depressed. Apex apparently central. 

 Surface marked by a nvimber of deep, concentric, irregiilar, sharp furrows, not always 

 continuous, and often breaking up into smaller grooves, and all these seem at times to be 

 impressed with lighter lines running nearly parallel with them.. Of the large furrows, 

 from nine to ten may usually be counted. The whole surface of the shell is marked by 

 a great number of delicate raised lines, radiating from the summit to the circumference, 

 and just visible to the naked eye. The shell appears to have been thin, and is probably 

 much compressed vertically." 



The defective material iu Professor Hartt's hands lias lead him to misapprehend some 

 of the characteristics of this shell. It is broadly elliptical or oval in outline, and is elevated, 

 especially at and in front of the apex ; the apex is acutely conical, pointed barkw ard, and 

 is about one third from the posterior margin. 



The following particulars may be added to Professor Hartt's description of this 

 species : — The lateral and posterior slopes of the shell are concave, especially near the apex ; 

 and the dorsal slope is convex and elevated in front of the apex. In the collapsed shells 

 preserved in the shales, this elevated portion is defined by a nan-ow ridge extending along 

 the dorsal line about one third or one quarter of the length of the shell, according to its 

 age; this ridge in the compressed shell often gives it the appearance of possessing two 



