HARDWICKE'S SCIENCE-GOSSIP. 



205 



two species are certainly Distylce, and his description 

 and figures as certainly indicate that genus. 



I observe that in his quotation of Mr Gosse's 

 remarks about Distyla, he omits the word lengthened. 

 Mr. Gosse says "the lengthened and flattened form." 

 The omission is of course unintentional, but the 

 character is important and fits Mr. Lord's species. 



As to the distinctions between the two genera, 

 these have been set forth in such a plain and concise 

 way in the criticism of Mr. Lord's article which 

 appeared in the December issue of the Journal of the 

 Royal Microscopical Society, that I may perhaps be 

 permitted to quote the sentence for the benefit of 

 those who have no opportunity of seeing the original. 

 " In Cathypna the whole trunk is loricated and the 

 creature when extended is dorsally arched ; but 

 in Distyla only the hinder portion of the trunk 

 is loricated, the forepart having a membranous 

 covering and the creature, when extended, is com- 

 paratively flat, or, as it is termed, depressed," Save 

 that the writer omits to draw attention to the usual 

 outline of the two genera when extended, Cathypna 



Fig. 184. — Monostyla arcuata. 

 Ventral view. X 320. 



Fig. 185.— Ditto, dorsal 

 view. 



being generally ovate, and Distyla of the form of a 

 long ellipse, the above sentence perfectly and briefly 

 summarises the points of difference. 



All other points in the generic characters are, I 

 think, either common to both genera, as "lorica 

 closed behind, toes two, selvage-like thickenings of 

 the lorica around the foot," or of secondary import- 

 ance as depending upon individual estimate, such as 

 lateral inangulation strong or feeble, or of habit, 

 such as " the habitual protrusion of the head " and 

 "the more constant activity." All these may be 

 safely disregarded, when there are present the 

 leading characters pointed out in the sentence 

 quoted. 



There appears to be some confusion as to the 

 meaning of the term lorica, in respect of the genus 

 Distyla. I am not myself quite clear that it ought to 

 be restricted to that portion of the covering of the 

 trunk, which appears to remain stiff and hard when 

 the animal is retracted. I have found that different 

 individuals of the same species do not always retract 

 to the same degree, that whilst at one time two short 

 lateral points (as described in many species) are 

 easily visible, at another time the retraction will be 



less complete and no points are to be seen ; and I 

 have found dead specimens of the same species, from 

 which the head and all interior parts have vanished, 

 yet displaying an apparently permanent shell much 

 exceeding that shown in retraction. I conclude that 

 the restricted use of the term may be convenient but 

 is possibly incorrect, and that the absence of the two 

 lateral points is a character that especially requires 

 careful verification. 



Although among some genera of the Rotifera mere 

 size is an unsafe guide to identification, there are 

 others in which, regard being had to mature 

 individuals only, the dimensions of the different 

 species are closely adhered to. Among the Cathy- 

 pnadae I have found the variation to be very slight, 

 not I think more than 10 per cent., if so much. It 

 would therefore be an assistance to those who hope 



Fig. zZi .—M onostyla. 

 cornuta. X 320. 



Fig. 1 86. — Distyla musicola. 

 Ventral aspect. X 480. 



to meet with Mr. Lord's forms, if he would state 

 particulars of the measurements when extended and 

 when retracted. It is also useful to know the exact 

 shape and length of the toes. There is in nearly 

 every genus, one point in which the species appear to 

 agree to differ. In the genus Macrotra.chela it is the 

 spurs, in Distyla and Cathypna the toes. 



I append descriptions of two species, which appear 

 to me very distinct from any of those yet described, 

 and of a Monostyla closely related to, but not identical 

 with, the common and well-known M. cornuta, 



Distyla depressa. 



Sp. Ch.— Lorica much flattened, ovate, truncate at 

 both ends ; anterior edges, ventral excised in moderate 

 curve, dorsal straight ; two short lateral points 

 shown in extreme retraction ; dorsal plate shorter 

 than ventral and narrower behind ; toes blade-shaped, 

 acute, slightly decurved ; brain three-lobed. 



