ENTOMOSTRACA OF MINNESOTA. 265 



spines; claws large, with a single basal tooth. The compound eye is 

 absent, its place being taken by the pigment fleck, which is the func- 

 tional eye.* 



*Monospilus teniiirostris Fischer. 



Plate LXII, Fig. 21, 21a. 



Fischer '54 (Lynceus tenuirostris); Sars '61; Norman and Brady '67; Mueller '68; 

 Hellich '77; Herrick '84 and '87 (dispar). 



Shell roundish; ventral margin setose; posterior angle rounded, 

 marked above with numerous impressions. Antennules small; anten- 

 nae long, with seven setse. Post-abdomen short and broad, bearing a 

 series of spines along the excavated posterior margin, and ornamented 

 on the sides with clusters of bristles. The shell in old individuals is 

 not moulted but remains as in Ilyocnjptns, covering the greater part 

 of the new shell. The figure shows an old individual with its succes- 

 sive coverings still clinging to it. Like Ilyocryptus, this animal passes 

 its life in filth at the bottom of pools and rarely emerges to the light 

 of day. What little visual function there may be is vested in the 

 larval organ. 



The specimen from which the drawing was made measured 0.45 

 mm. The first glance at this rarest of all entomostraca affords proof 

 of its unique character. The strongly arched shell is so compressed 

 as to bear little resemblance to Chydorus. The dorsal line passes with 

 little angle into the high posterior margin. There is a rounded angle 

 below, armed with two teeth — the shortened representatives of the 

 fringing spines of the straight lower margin. The head is depressed 

 and very short; but the narrow beak is produced to below the margin 

 of the valves. It is rounded so as to resemble, as seen in front, a duck's 

 bill. The fornices are narrow and flare so that the eye is left partly 

 exposed upon the side. The antennules are not long but slender. 

 The labrum has a very large lamella, which is crenulate in front and 

 acute below, the labrum proper being large. The systematic position 

 of this genus is a matter of considerable interest, for it is the only 

 member of the whole order in which the larval eye is the only one 



* So much Interest attaches to this species that we reproduce the latin description of Sars: " Testa 

 in adultibus valvulis composita pluribus, altera alteri imposita, a latere visa lata, latitudine maxima in 

 parte antica sita; margine superiore autice valde prominente, posteriore et inferiore ciliato rotundatis. 

 Caput mobile, perparvum et valde depressum, supine impressione parva sed distincta, a testa cetera dis- 

 junctum, deorsum in rostrum rectum et breve apice obtuso exiens. Animal supra visum sat compressum, 

 latitudine maxima capite majore ante medium sita. Pars superior test;e et capitis impressionibus nume- 

 rosis rotundatis notata. Anteanis 1-mi paris minuta' structura ut in ceteris Lynceidis; 2-di paris sat 

 longte, ramo altero setas 4 et aculeum unum apicalem altero setas 3 et aculeos duos, quorum alter longus 

 articulo prime ejusdem rami adfixus est.gerunte. Post abdomen breve et latum, apicem versus truncatum; 

 margine posteriore supra obtuse angulato, ad angulum inferiorem rotundatum seriebus duabus aculeo- 

 rum inque lateribus setis vel spinulis brevibus numerosis praditum; ungues terminales ad basin aculeo 

 longo armati. Intestinum, ut in ceteris Lynceidis, in thorace laquem fere duplicem format. Macula 

 nigra unica minima prope basin antennarum 2-di paris; macula? infra oculari in ceteris Lynceidis 

 simillima, in capite conspicitur, quK, quum oculus verus compositus in omnibus ceteris Crustaceis Cla- 

 doceris distinctus omnino absit, organum quamquam rudimentare visus habenda est. Animal parum 

 pellucidum, colore fulvescente. Longit. parum supra ^3 mm." 



