284 96 



I found the species in enormous masses in a little lake: Klareso near Helle- 

 bæk, North Seeland; there were many pelagic eggs found by Zacharias (1893, p. 35) 

 and Apstein (1896, p. 160). Male eggs were not observed. In the samples which be- 

 sides contained only Rattulus stylatus. Brachionus militaris, Polyarthra plahjptera, 

 Synchœta pectinata and Gastropus stylifer, the male was rather common; it was 

 unquestionably hatched in my vessels and could not be referred to other species 

 than Ploesoma. which was the most common species. 



Gastropodidæ. 



In mv opinion the fam. Gastropodidæ comprises the four species: G. ckandaius 

 (Ehrbg), G. hgptopus (Ehrbg), G. minor Rouss. and G. stylifer Imh. Of these species 

 G. claimlatas and G. hyptopus together with Xotops brachionus are referred to the 

 genus Xotops under the fam. Hijdatinidce. In the descriptions I find but very little 

 conformity between these two first named species, but as I have never had the 

 good luck to find the large and rare G. clauulatus I do not venture to alter their 

 svstematical position. If my supposition should be correct the genus Gastropus should 

 be divided into two genera one of which should contain G. clauulatus and G. hyp- 

 topus, the other G. minor and G. stylifer. 



The males of this family have hitherto been almost wholly unknown; there 

 exists a veni' curson.' sketch of the male of G. clauulatus by Western, and a figure 

 and description of G. hyptopus by Wesché, but this differs very much from that 

 which I shall give in the following pages. 



Gastropus clavulatus (Ehrbg.). 

 = Notops cla\Talatus Ehrbg. 

 Male: "Western. 1892, p. 374. 

 Western (1892, p. 374, PI. 25. fig. 6)has given the following description of the male: 

 The general contour is that of the female even to the deep furrow at the posterior 

 extremity. . . . There is no sign of the foot; the digestive organs are totally absent. No vas- 

 cular canal, vibratile tags and contractile vesicle are obser^'ed. A large sperm-sack. A large 

 ganglion or brain carries an eye spot on its ventral side, and numerous ner\e fibres may be 

 traced from it to various parts of the body. The males were hatched from small white eggs. 

 Size V-io. 



Gastropus hyptopus (Ehrbg.). 



= Xotops h>"ptopus Ehrbg. 



Male: Wesché Uiu2, p. 327. 

 Tab. VI, flg. 3—5. 



Wesché (1902, p. 327, PL 17, fig. 3) gives the following description of the male: 



'The male has much the same shape as the female, i. e. a rather globular sack. The 

 head is defined by folds of skin which can be traced on the surface. The body is globose, 

 \s"ith a tough skin, which it requires some imagination to describe as lorica. There is the folds 

 of skin on the dorsum. Strictly speaking the foot is absent, but its place is occupied by the 

 penis. The cilia are very long and filiform. The brain is exceedingly large, and comes down 



i 



