CEPHALASPID^.. 



51 



denticular processes are very apt to get lost and obscured in these fossils, as, for example, 

 those on the inner edge of the cornua of the common Eucephalaspis J^assizii. Perhaps 

 this species may be merely a larger growth of C. Pagei, the spinets being preserved in 

 the large specimens, but undeveloped or obscured in the smaller. Nevertheless, it is 

 right to signalise this characteristic structure by a name. Further search in regard to 

 this and other similarly dubious matters indicated in these pages is required, and the 

 matter is best pressed on the attention of collectors and others by provisionally naming 

 the supposed species. The horror with which the making of a species on small data is 

 regarded by some naturahsts appears to be a superstition which may lead to evil results, 

 for the opposite proceeding of passing over all differences and indications of distinction 

 among forms, unless of the most certain and obvious character, is far more injurious to 

 the progress of knowledge. The use of a name, whether of genus, species, family, or what 

 not, is merely to briefly draw the attention to a supposed speciality of structure separating 

 the individuals, to which the name is applied, from others. There is nothing sacred in a 

 name, and, if the progress of discovery render it desirable, old names can be changed or 

 supi)rcssed. As long as the data on which a species is named are fairly and fvdly stated, it 

 can be no encumbrance to science, even though it should eventually prove to be not 

 distinct from another form. 



6. Hemicyclaspis Murchiso^i. pi. VIII, fig. G ; PI. IX, fig. 1 ; PI. XII, figs. 3 and 4. 



Cepiialasi'is Murchisom, Egerton. Quart. Jouni. Geol. Soc, vol. xiii, p. 284,pl.ix, 1857. 

 — ORNATUS, Id. Ibid. 



Name. — After Sir Roderick Impey Murchison, Bart. 

 Siratigraphical Position. — Tilestones and Auchenaspis-grits. 



Characters. — The woodcut (fig. 24) presents the characteristic outline of the sub-genus 

 and the ornament which characterises the species. The tubercles ornamenting the surface 

 arc arranged in distinct groups, marked out as polygonal arese, in this species, more 

 distinctly than in C. Pagei, some distance of intertubercular surface intervening between 

 the contiguous groups. 



General Remarks. — Sir Philip Egerton (loc. cit.) described C. Murchisoni and 

 C. ornattis originally as two distinct species, suggesting, however, that they might prove 

 to be identical should specimens of C. Murchisoni showing the surface be discovered. 

 I have received such a specimen from Dr. Grindrod, and do not doubt that the two specimens 

 figured from the Tilestones near Ludlow and the two from the Ledbury Grits are the same 

 species. A question was also raised by Sir Philip as to whether C. Murchisoni might 

 not belong to his genus Auchenaspis, being thus the anterior portion of a shield divided 

 into head- and neck-plates. The presence of a groove running parallel to the edge of 

 the semicircular shield seems to me to oppose this notion, for a similar groove runs 



