STATE GEOLOGIST. 141 



(b) var. similis, (Var. n.) 

 (Plate Q. ' Figs. 5—7.) 



This form is twice as large as D. leptopus, but otherwise scarcely 

 distiDguisliable. It occurs in autumn (and spring?) in shallow 

 pools, which can but be frozen solid. The following diflPerences 

 are the only points yet noticed. Females of both of the species 

 were placed side by side upon a slide and examined. D. leptopus 

 measured 2.4 mm., exclusive of caudal setae; the antennae reached 

 hardly to the base of the stylets; the eggs measured 0.12 mm., while 

 those of D. longicornis measured 0.8 mm.; the egg-sac measured 

 0.8 mm., while that of longicornis was 0.5 mm. A few other minute 

 differences were noticed, but the general form and color was iden- 

 tical. The peculiar doubling of the edge of the last segment is 

 characteristic of these two forms; each has a small spine on either 

 side of the abdomen. The base of the inner ramus of left foot of 

 fifth pair of the male has a double series of spines. 



Sp. 7» Diaptomiis laticeps, Bars. 



"Cephalothorax aLtice dilatatus. latidudine maxima in pane antica capitis sita, 

 postice sensim atteuuatus, segmento ultimo feminae ad latera parum extante angulis 

 lateralibus acuminatis. Segmentuni 1-mum abdominale feminse antice latum mucrone 

 brevi laterali armatum, postice sensim attenuatum. Rami caudales sat magni seg- 

 menta antecentia 2 juncta longitudine-sequantes setis brevissimis et robustis instruct!. 

 Antennse l-mi paris feminge longltudinem corporis requantes, anlmali natante rectte et 

 quam in D. gracili adliuc magis postice vergeates ; articulus antepenultimus antennae 

 dextrse maris liamulo armatus. Ramus exterior auteunarum 2-di paris interiore multo 

 longior articulo ultimo longitudiuem articulorum autioedentium 5 aequante. Pedum 

 5-ti paris feminae articulus ultimus parvus, cylindricus, nou vero tam rudimentaris 

 quam in D. castore, aculeo uno brevi apicali instructus ; appendix interna ne tertiam 

 quidem longitudinis articuli 3-ti partem aequans et uniarticulata ; pedis dextrl maris 

 articulus 3-tlus extrorsum aculeo forti armatus, ungue terminali valde flexuoso et sub- 

 sigmoides ; sinister aculeis duobus rectis terminatus. Saccus oviferus sat multa conti- 

 netova. Color pleurumque laete cseruleus, interdum pallidior, albescens. Longit. 

 feminse circit. Wz mm." 



Sp. 8. Diaptonius gracilis, Sars. 



"Corpus quam in D. castore gracillus, ceplialothorace et antice et postice attenuato, 

 latitudine maxima in medio sita. Anguli laminarum segment! ultimi thoracalis femi- 

 nge in mucrones tenues et acuminatos product!, et mucrone simili sat magno segmen- 

 tum 1-mum abdominale utrinque armatus est. Rami abdominales breves setis in fe- 

 mlna valde divergentibus. Antennae l-mi paris feminae perlongae et tenues, longitudi- 

 uem totius animalis longe superantes, anlmali natanti rectae et aliquantum postice ver- 

 gentes ; articulus antepenultimus antennae dextrne maris liamulo longior, articulo ultiuio 

 rami dimidium longitudiuem aequaute. Pedum 5-ti paris femlnae articulus ultimus rti- 

 stinctus, quadratus aculeis duobus apicalibus quorum interior apicem fere unguis arti- 

 culi penultimi attingit instructus ; appendix interna articulo 3-tio brevior ; unguis ter- 

 minalis pedis dextri maris apicem versus valde curvatus. Saccus oviferus semper ova 

 cuntinet paucissima et niagua regulariterque distributa. Animal pleurumque pelluci- 



