82 MR. GEOFFREY WATK.1N SMITH ON THE 



SiMOCEi'HALUS australiensis, Dana, United States Exploring Expedition, Crustacea, 

 ii. ]>. 1271; also Sars, Eorhandlingor, Cbristiania, 1888, p. 15. 



This species can be readily distinguished from the foregoing by the distinct projection 

 on Hie underside of the head just in front of the insertion of the first antennae (PI. 15. 

 fig. S), and also by the form of the telson, which has the anal claws armed with a 

 conspicuous row of spines at their bases (PI. 15. tig. 9). There is a good deal of variation 

 in the shape of the hind part of the carapace, the posterior angle being sometimes 

 pronounced and sometimes almost absent. 



The species occurs in quite small puddles and ponds, and is evidently universally 

 distributed in Tasmania. Dana and Sars report it from near Sydney. 



Genus Dapiinta, O. F. Midler. 



Daiminia caiunata, King, Proc. Roy. Soc. Tasmania, 1853, p. 253. 



This species was found by Mr. King in the neighbourhood of Sydney. 



I found some very largo specimens, measuring 3 millimetres in length, in a few cupfuls 

 of water in a cart-rut near Plenty, Tasmania. These specimens were among the tubes 

 in my collection that were destroyed, so that I cannot give a lull description of them. 

 They agree, however, with King's figure of D. carinata, variety C, in having the spine 

 at the back of the carapace very short. 



Family Bosminidj! (Sars). 



Genus Posmina (Paird). 



The three speoies described below, which are the only Bosminidrc hitherto found in 

 Australasia, arc closely related to the common northern B. lonyirosl ris. They possibly 

 only represent varieties of one species. 



POSMINA ROTUNDA, Sp. n. (PI. 15. fig. 18.) 



Female. — Form of the carapace very round, with the posterior angle not distinctly 

 marked. A seta is present on each valve close to the posterior spine. There is a 

 slight projection whore the forehead passes into the first antennae. 



The first antemue are long, slightly curved, and with about eleven joints below the 

 antenna! spine and sensory seta'. 



The second antennas are short and do not project as far as the anterior angles of the 

 valves of the carapace ; their structure is normal. 



The anal claws aro long, and carry about four small spines near their base ; the telsonic 

 angle is furnished with about three rows of small bristles. 



Length 9 mm. 



Colour. GrcoD. 



Occurrence. In the plankton of Lake St. Clair. Males were not observed. 



