SPT ere ae TEEN ty a AR 
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 tenuirostris Fischer. 
PLATE LXII, Fie. 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- 
ne long, with seven setz. 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 Jlyocryptus, covering the greater part 
of the new shell. The figure shows an old individual with its succes- 
sive coverings still clinging to it. Like Zlyocryptus, 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 positioa 
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 antice valde prominente, posteriore et inferiore ciliato rotundatis. 
Caput mobile, perparvum et valde depressum, supine impressione parva sed distincta, a testa cétera 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 et capitis impressionibus nume- 
rosis rotundatis notata. Antenne 1-mi paris minute structura ut in ceteris Lynceidis; 2-di paris sat 
long, ramo altero setas 4 et aculeum unum apicalem altero setas 3 et aculeos duos,quorum alter longus 
articulo primo ejusdem rami adfixus est, gerunte, Postabdomen 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 preditum; 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; macule infra oculariin ceteris Lynceidis 
simillima, in capite conspicitur, que, 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 +4 mm,” 
