496 DK. A. W. EOWE ON THE GENUS MICRASTEK. [Aug. 1899^ 



when they are useful as zonal guides, by varietal titles, we could 

 then readily build up a scheme, which might have some zoological 

 value, wherein specific and varietal names would be descriptive 

 both of shape and horizon, thus enabling us to abolish such bar- 

 barisms as cor-anguinum and cor-testudinarium. But the law of 

 priority is unyielding, and we must accept, with the best grace 

 that we may, such anomalies as the raising of the high-zonal 

 Micraster cor-anguinum aud the low-zonal M. cor-testudinarium to 

 the level of specific types, while their low-zonal ancestor, M. proecur- 

 sor (p. 530),^ which is equally important and abundant, is obscured 

 by a cloud of specific names. 



The grievance is very real, for it is hard to have to tack on 

 a varietal name to such a polysyllabic enormity as Micraster cor- 

 anguinum, and yet that is just what has to be done, in order that 

 we may mark an essential horizonal type. 



^ [As there is a probability of this name being adopted in the future as 

 specific, it may be well to point out that, though the extreme forms graduate 

 into M. Leskei, on the one hand, and into M. coT-testudinarium on the other, 

 yet the intermediate series is as distinct as in many accepted species, the 

 extremes of which are well known to graduate into other forms, but are never- 

 theless accepted as valid species. 



Although, primarily, I have designed M. prcecursor in the broad sense as a 

 group-name, it is also used in the restricted sense, when dealing with the form as 

 it occurs in the various zones. lespecially state that, even in its restricted 

 sense, it cannot rightly be called a species, as it is merely the same 

 form, or series of contour-forms, impressed with certain special features of the 

 test, which are peculiar to each individual zone, and therefore varying in detail 

 from zone to zone. A group-name which embraces so Protean a series as 

 this can hardly be called, from a zoological standpoint, a true species ; and yet, 

 by usage and for the needs of classification, it is probable that it will be used in 

 a specific sense, however much I may demur against such a course. 



M. prcBcursor is only the dominant form of the narrow low-zonal type, just as 

 M. cor-anguinum is the dominant form of the narrow high-zonal type. Neither 

 of them has any valid claim to a true specific title, save that of convenience. 

 If it be right to preserve M. cor-anguinum as a species, it is equally I'ight to use 

 M. prcBCursor in the same sense. These particular forms must have a name, and 

 precursor serves that purpose as well as any other. Assuming that M. pracitrsor 

 will be used, for convenience, as a species, it will be necessary to define it roughly, 

 though it is impossible, on account of its zonal variations, to give a diagnosis 

 which shall be at once accurate and concise. 



While the smaller and narrower forms of M. precursor agree in general 

 outline, position of disc, position of peristome, and shallowness of ambital notch 

 with M. Leskei, they differ from this species in having a varying degree of 

 ornamentation of the interporiferous area, ranging from the 'sutured' to the 

 'subdivided' type, instead of a perfectly smooth area. Further, the anterior 

 peristomal segment is always broad and jointed in M. prcecursor, and the 

 labral plate more or less freely tuberculated. The converse holds good in 

 M. Leskei. 



On the other hand, M. prcecursor differs from il/. cor-testudinarium, Gldf., in 

 being narrower and, as a general rule, smaller. We have here no type of ambu- 

 lacrum which is singular to one form, as in the case of M. Leskei, for all the types 

 of ambulacra, from ' sutured ' to * subdivided,' are shared by M. prcecursor and 

 M. cor-testudinarium alike. It may be stated, however, that according to the 

 rule that broad forms have deep ambulacra, we find that, on the whole, M. cor- 

 testudinarium has deeper ambulacra than M. prcecursor, and that, owing to the 

 increased depth, the subdivided ambulacra are mostly associated with the broad 

 ioxm.—June 7th, 1899.] 



