160 Mr. J. W. Salter on new Fossil Crustacea 



the specific name (as Prof. M'Coy supposed) of Cultellust rectus, 

 but I accept the term ; and as the subyenera of Solen are not 

 very likely to be found in Silurian rocks, it had better be called 

 Solen rectus. It is perhaps quite as much like Ceratiosolen. 



Prof. M'Coy has rejected it from this society, and figured it 

 with the form and lineation of Ceratiocaris, with a thickened 

 ventral margin and with an eye-spot. A careful examination of 

 fresh specimens convinces me, however, that he has been mis- 

 taken in these characters. 



Moreover, the general form is so like that of one of iheSolenidte, 

 that it would seem to require something more than close criti- 

 cism to refer it to anything else. The anterior side is rounded 

 off, and the posterior truncate. There is even' a slight fold 

 along the dorsal margin a character very common in bivalve 

 shells; and lastly, there are a few concentric ridges of growth 

 on the posterior side, while the disk only is occupied with close 

 and numerous stria? parallel to the edge. These striae have appa- 

 rently misled Prof. M'Coy, who supposed that they covered the 

 whole surface, as in Ceratiocaris. Moreover the internal oblique 

 ridge extending backwards from the beak is no uncommon 

 character of the Solenidce, Prof. M'Coy supposed it to be the 

 nuchal furrow. 



Not having till now had access to good specimens, I for some 

 time thought its new association with Crustacea correct ; and 

 I catalogued it as a Ceratiocaris in ( Siluria/ 2nd ed. Appendix, 

 p. 538 ; it is, however, necessary to restore it to the Mollusca. 



I believe there are other forms of the genus even in Britain, 

 besides these nine or ten species which have all turned up in 

 the course of a year or two. Abroad, still larger specimens have 

 been found in Upper Silurian rocks. M. Barrande has figured 

 the tail-spines of three species, of which his Leptoc. bohemicus 

 has the greatest resemblance to our C. Murchisoni ; and> as 

 above noted, a large species, C. Dewii, has been figured as a fish- 

 defence by Hall, from the Niagara limestone of New York. Our 

 own Dudley limestone contains one species ; but the metropolis 

 of this curious Silurian ( shrimp ' is in the Lower Ludlow 

 rock, where it keeps company with Pterygoti and other large 

 Crustacea. It appears not to have been a long-lived genus, for 

 as yet none have been detected below the Werilock limestone or 

 above the Upper Ludlow rock. I should perhaps except a frag- 

 ment of a large carapace sent me from the Llandeilo flags ? of 

 Dumfries by my friend Prof. Harkness. But the rock and the 

 fossil both bear such a suspicious resemblance to the specimens 

 of C. stygius, that I wait for better evidence before admitting the 

 existence of the genus so far back in time. However, a much 



