MR. S. HA-IfLET ON NEW SPECIES OF DONAX. 539 



related cases of partbenogenesis among tlie Acari. Both hy- 

 potheses are therefore supported by analogy from a related 

 group. Unfortunately, disintegration has prevented a satisfac- 

 tory examination of the spermathecse of the Spider in question ; 

 but I am inclined to believe tliat the case is one of agamic 

 reproduction, inasmuch as I can find no lumen in the exuvia 

 through which impregnation could have taken place. Bertkau 

 states (" TJeber den Generationsapparat der Araneiden," Archiv 

 fiir Naturgesch., vol. 1, year 41, p. 253) : — " Nur so viel ist ge- 

 wiss, dass die Spinnen mit oder nach der letzten Hautung 

 geschlechtsreif werden." 



I purpose to continue my investigations on this subject, and 

 hope that others may do the same. 



Description of nevs^ Species of Donax in the Collection of the 

 Author. By Stlvanus Hanlet, P.L.S. 



[Read June 1, 1882.] 

 (Plate XII.) 



Since 1843, when I first described three new species of Donax, 

 four important monographs have appeared of this now large genus. 

 The first, by Eeeve, strangely ignored the paper I. had published 

 in the ' Proceedings of the Zoological Society ' for 1845, but 

 figured the same specimens with the same names from the Cumin- 

 gian collection. The last, and critically the best, is the post- 

 humous production of the late Victor Bertin, who declares that 

 both Eeeve and Sowerby have wrongly delineated my Donax assi- 

 milis. Premising, therefore, that the Donaces which follow cannot 

 even be regarded as varieties of any delineated in the four mono- 

 graphs above alluded to (so peculiar are they in their form and 

 proportions), I will proceed to describe them : — 



Donax Mesodesmoides, n. sp. (Plate XII. fig. 1.) 

 T. magna, valida, oblonga, satis convexa, curvato-subcuneiformis, 

 valde insequilateralis, nitida, Isevis, sub epidermide cinereo-flaves- 

 cente extus omnino Candida, intus prsecipue purpurascens ; lateris 

 antici extremitas attenuato-rotundata, lateris postici rotundato- 

 subtruncata. Area postica angusta rugis ereclis flexuosis sub- 

 remotis transversis, lineisque radiantibus humilioribus decussata. 

 Margo dorsalis antice incurvatus, modice declivis ; margo ven- 



