4 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 78 



Family ATELECYCLIDAE 

 MONTEZUMELLA, new genus 



AtelecycUdae nov. gen. Glaessne^!, Fossilium Catalogus, 1, part 41, 1929, p. 446. 



In shape and ornamentation of carapace resembling Erimacrus^ 

 but differing in the orbit which is broadly tubular viewed from above, 

 concealing the eye. Postero-lateral margins of carapace unarmed. 

 Cancer fraasi Lorenthey " belongs apparently in this genus and may 

 be known as Montezumclla fraasi. 



MONTEZUMELLA TUBULATA. new species 



Plate 2 



Description. — Carapace suborbicular, a little longer than wide, 

 widest at the middle ; f ronto-orbital distance great, more so than the 

 posterior margin. Regions plainly indicated by broad furrows, gas- 

 tric region divided into subregions, a curved furrow on the anterior 

 branchial region. On the anterior half of the hepatic region there 

 is a small, low, conical elevation. The mesogastric region is con- 

 tinued to the frontal margin, where it is depressed below the neigh- 

 boring surface ; parallel to the mesogastric furrows there is on each 

 side a shallow groove leading from the outer margin of the subme- 

 dian frontal tooth. The dorsal surface is covered with irregular 

 tubercles or large granules. The fronto-orbital and antero-lateral 

 margins are dentate, the teeth that remain being denticulate, each 

 denticle tipped with a short, stout, movable spine. The median sinus 

 of the front is deep U-form; on either side is a transversely oblong, 

 ascending tooth each with 3 denticles at the extremity and an indi- 

 cation of one on the inner margin. Next to the submedian tooth and 

 separated by a sinus narrower than the median one, there is an inner 

 orbital tooth, rectangular in cross -section,^ low and broad, and armed 

 with 4 divergent spines, A broad rounded sinus separates this tooth 

 from the outer orbital tooth or lamina; this is very broad, its free 

 margin forming part of the antero-lateral slope; on the dorsal sur- 

 face there is a closed fissure at the outer third ; the free edge is spined. 

 A cross-section of the orbit is shown on the left side ; it is broad ob- 

 long with the corners rounded; the eye is short and stout. The 4 

 antero-lateral teeth of the carapace are known only from cross-sec- 

 tions (pi. 2, fig. 1) ; the third is the widest, the first and second of 

 subequal width, the fourth narrow and thicker than the others. 

 Lower surface of carapace granulate, the granules running smaller 

 and closer than on the dorsum. Pterygostomian region and ster- 



• Math.-natuiw. Ber. aus Ungain, vol. 25, 1907 (1909), p. 141, pL 2, figs. 3a and 36. 

 '' Shown in plate 2, figure 2, on the left side. 



