OASTROI-OI'A v -'7 



in his genus Tryblidium with the specific name naH'itum. It is very closely related 

 to our // I ii fortunately we know very little of the muscular scars of these 



species, so that it is difficult to decide whether their affinities are nearer Tryblidium 

 'In. What is known of them agrees better, as does also the form of the 

 shells, with -i ..... ics of the former genus, while they are distinguished from both by 

 the distinct radial sculpture of their surfaces. The marginal position of the apex 

 separates them from Scenclla, Billings. Stenolheca, Salter, includes laterally 

 compressed and much higher shells. 



The generic name is from the external resemblance which the species bear to 

 the recent species of the genus Helcion, Montfort 



1 1 H.riONOPSIS 8TRIATA, . */). (UlHrli.) 



PLATE (.XI. FIOS. 39 ndaO. 



Shell rather strongly convex, acuminate-ovate in outline, broadly and regularly 

 rounded behind, pointed in front where the apex projects slightly beyond the margin 

 of the aperture; apex incurved. Surface marked by distinct, rounded, radiating 

 lines, which in the outer half maintain an approximately equal size through 

 In furcation; about ten lines in 5 mm.; whole surface with very fine concentric lines; 

 at intervals of 1 to 3 mm. irregular wrinkles marking stages of growth. Length 

 Ji '. mm.: width about 19 mm.; greatest bight 9 ram.; bight of apex about 4.5 mm. 



This species is quite distinct from all American patelliform shells, but is closely 

 related to the Upper Silurian //. r<i<lin/<i LindstrOm sp.* As figured that species is 

 a little more convex, the anterior outline blunter and the apex more incurved. 



Formation and locality Rare In the upper beds of the Cincinnati formation, Marlon county, 

 K--II!-I.-'K> Also, though of smaller lz-, in th- L.raln<> jfroupat Cincinnati. Ohio. 



CWtatfoi.-E. O. I 'I rich 



-TBCAKINATA. ;/. sp. 

 ATt i \! no. a. 



il Miiall. MiLovate in outline, the anterior and posterior margins subequal 

 and sharply rounded in the middle. In the cast the apex is depressed, small and 

 not quite marginal; an olitu-*; (-urination extends across the length of the shell. 

 Surface of cast showing remains of very fine radiating lines, scarcely visible without 

 a magnifier, and a few obscure lines of growth. Length 10 mm.; width 8 nun.; 

 greatest hight -V mm.: hight of apex l.."i mm. 



We have only two specimens of this interesting species. Both are casts and 

 show impressions of the rostral muscles. One exhibits besides a series of muscular 

 scars similar to those of Trybli-linm. The lines converging from them towards the 



SlluriM O..lropod *d PUroptxU of GoiUnd. p. M; IM. 



