372 Viscount (I'Archiac and M. de Vekneuil's 



3. Orthis Lepis, nob. Strophomena lepis, Bronn, Leth. Geog., PI. II. f. 7. Productus elegans, Hupsch, 



Natur. Nieder. Deutschl., PI. I. f.7, 8. Isis, 1825, 12'^ Cahier, PI. XIII. Stein. Mem. de la Soc. 

 Geol. de France, i. p. 361. Tab. nost., XXXVI. f. 4, 4 a. 



We have to remark upon this species, that the straight hinge is very nearly equal to the width of the 

 shell, and that it is composed of two very distinct and much elongated areas. Upon the middle of each 

 area there is a triangular fissure, remarkable for its smallness in proportion to the shell. These fissures 

 are usually closed, and are one-third of a millim. in width. 



The O. Lepis differs from Leptcena transver sails, Dalm., Orthis transversalis, de Buch, in its still more 

 transverse and less elongated form, and by the dilatation of the lateral edges, which, in the L. traits- 

 versalis, have a tendency to approximate in descending toward the front. 



The form of O. Lepis being the same as that of the Producti, it is not surprising that it should have 

 been placed in that genus, to which Dalman gave the name of Leptcena. In some individuals where the 

 area is still more contracted it becomes almost impossible to perceive the fissure. Those species called 

 Leptcena by the Danish naturalist, and even by J. Sowerby in Murchison's Silurian System, form the true 

 connecting links with the Producti, in which the area and the triangular fissure are no longer discernible. 



4. Orthis subarachnoidea, nob. (O. arachnoidea, Phill. Pal. Fos., PL XXVII. f. 114, non Spirifer; id. 



Geol. Yorks., Part 2, PI. XI. f. 4.), Tab. nost., XXXVI. f. 3. 



Shell depressed ; dorsal valve presenting the form of an ellipsis truncated by the cardinal line, which 



is straight, and as wide as the shell. The lateral edges, at right angles to the hinge, are rounded, 



and coalesce with the front so as to describe three-fourths of a regular ellipsis. Fine and deep 



striae (perhaps granular at their extremities) set off" from the beak and radiate toward the edges, 



being subdivided several times. Ventral valve unknown. Length, 60 millim. ; width, 48. 



This species has some analogy with the Sp. arachnoidea, Phill. (Geol. of Yorksh., Part 2, PI. XI. 



f. 4.), but as this author only gives the upper valve, which we have not, we have not yet thought proper 



to consider as identical shells so incompletely known, and which, furthermore, belong to very different 



geological systems. 



Grauwacke of Kemmenau and Ems. It is found also in Devonshire. 



5. Orthis minuta, Goldf. De Buch, Mem. de la Soc. Geol. de France, t. iv. p. 217, Tab. nost., XXXVI. 



f. 5, 5 a, 5 b. 



Shell nearly hemispherical, presenting on each valve twenty-one very distinct radiating ribs, which 

 are simple, or I'arely bifurcate. Hinge straight. Ventral valve semicircular, concave, particularly 

 under the beak. I-ateral edges forming an angle of 110° with the hinge. Median apophysis, sa- 

 lient upon the area above the beak. Dorsal valve ventricose, beak very much recurved and some- 

 what ventricose. Area very narrow, concave. Aperture very small, closed, and partly covered by 

 the apophysis of the other valve. Length, 12 millim.; width, 13; thickness, 6. 



Eifel. 



Pecten Hasbachii, nob.. Tab. nost., XXXVI. f. 13. 



The only fragment we possess of this shell is so incomplete that we cannot determine all the cha- 

 racters of the species, nevertheless it has furnished us with a suflScient number to enable us to distinguish 

 it from all others of the same genus that have yet been found in the older beds, and to decide us to give 

 a representation of it. 



The radiating ribs, which were in number from eighteen to twenty, are wide, flattened, and divided into 

 two, three or four, by grooves which continue almost to the beaks. The grooves which separate the ribs 

 are concave, and sometimes have one or two obsolete folds. 



Refrath ; very rare. 



