CRUSTACEANS 



this record of seven species published by Professor Carr may now be added, from Mr. C. E. 

 Pearson's collection, the interesting species Porcellio dilatatus (Brandt and Ratzeburg). From 

 P. scaber this is distinguished by its broader shape, less tuberculose integument, and the produced 

 rounded (not acute) apex of the telsonic segment. Also in the second antennae the two 

 joints of the flagellum are about equal in length. Bate and Westwood record it only from 

 Ireland, and say it is found among decaying grass and straw, and appears to be extremely 

 rare. 1 But like many other rarities, it has proved to be not so very uncommon when search 

 is conducted with a little pertinacity. Though the Oniscidea more than ever withdraw them- 

 selves from the public gaze during our English winter, Mr. C. E. Pearson was able in a few 

 days of January and February to collect for me from Lowdham and Chilwell, besides the 

 above-mentioned P. dilatatus, also P. scaber ; the straight-fronted, smooth-coated Metoponorthus 

 pruinosus ; and the globe-forming Armadillldium vulgare, including prettily-marked specimens 

 of the form known as var. vent gat a. 



From the Malacostraca, in which a strong cord of uniformity binds together all the diverse 

 elements, we now pass to the Entomostraca, united indeed to the other sub-class and united 

 among themselves, but united by less evident and more entangled threads. For species 

 occurring within this county I am indebted to papers by Mr. Edwin Smith, M.A., published 

 in The Midland Naturalist* and to an unpublished list by Mr. W. H. Pratt, F.R.M.S., of 

 Cavendish Hill, Sherwood, Nottingham, sent me through Professor Carr, to whom I am 

 further indebted for the published record of one species and for specimens of another. From 

 these several sources sixteen or seventeen species, illustrating the three orders of the sub-class, 

 can be accredited to the county. The orders in question are named Branchiopoda, Ostracoda, 

 and Copepoda, in allusion to features which are more or less conspicuously characteristic of 

 them severally. The names signify respectively gill-footed, valve-shelled, oar-footed. It is in 

 the last of these groups that we find forms the most shrimp-like, the least remote from the 

 Malacostracan pattern. Mr. Edwin Smith, in the work already cited, gives an interesting dis- 

 cussion of the Copepoda, taking as a type the species Cyclops quadricornis from some unspecified 

 locality. Mr. Pratt records it from ' ponds and ditches about Nottingham in many places,' 

 and the same authority records Canthocamptus minutus from ' pond at Gamston near Notting- 

 ham.' In regard to this and two other species Mr. Smith makes the following remarks, some 

 of which will be useful for wider application : ' Nearly allied to Cyclops, and not much unlike 

 it in appearance, is Canthocamptus, found abundantly in the ponds about Nottingham. As it 

 is rather small, the best way to secure a specimen for examination is to place a portion of the 

 gathering in a shallow dish and look it well over with a pocket lens. A small dipping tube, 

 made as follows, will be found useful : One end must be drawn to a blunt point with moderate 

 aperture, the other inserted into a short piece of india-rubber tubing sealed air-tight at the free 

 extremity. Press the india-rubber between thumb and fore-finger, dip into the water, and by 

 removing pressure at the right moment the object is sucked up into the tube, whence it may be 

 expelled by once more pinching the indiarubber. The two commonest species of Cantho- 

 camptus are C. minutus and C. furcatus. In the female I have often found a curious reddish 

 substance coming off from the sixth body segment. It is of a hard and horny nature, but its 

 use is not known. Closely allied to the preceding is Diaptomus castor, easily recognized by its 

 inferior antennae, which are fully as long as the entire body. I have found it amongst algas in 

 stagnant ponds.' 3 



Thus we have apparently four species of normal Copepoda to deal with. As already 

 indicated, they are extremely common species. Also they are all insignificant in size, but the 

 three genera belong to three different families, of which the Cyclopidae and Arpacticidas belong 

 to the division Podoplea, the Diaptomidae to the division Gymnoplea. To explain this sever- 

 ance we have to notice that the framework of ordinary Copepoda is divided into eleven 

 segments, the first or cephalic being composite. This is followed by a middle-body or limb- 

 bearing trunk of five segments, and a pleon or tail-part of five segments without limbs. In 

 the Gymnoplea, as the name implies, there is a bare or naked pleon, in the sense that the pleon 

 is devoid of limbs. But in the Podoplea the pleon seems to have annexed one of the limb- 

 bearing segments of the middle-body, and hence the name of the division, implying that the 

 pleon carries limbs, points only to a difference which is apparent rather than real. It would 

 often be delightful if natural history could tell its story in the compendium of a single word, 



1 Brit. Sess. Crust, ii, 479. 



8 Op. cit. No. I, January, p. 15 ; No. 2, February, pp. 33-37, vol. i (1878). 



8 Op. cit. 34. 



147 



