AVICULIDA. 273 
terior teeth laminar, elongated; anterior (pedal) scar deep 
posterior (adductor) impression large, very excentric. 
PrERONITES, M’Coy, 1844. Shell thinner, subtriangular, with 
the teeth less developed. P. angustatus, M’Coy. 
EOPTERIA, Billings. (?Euchasma, Billings.) Valves equally 
convex, hinge with an external (?) lig: ament. P. typica, Billings. 
Lower Silurian ; Newfoundland. 
ACTINOPTERA, Hall, 1883. Differs from Pterinea in the absence 
of striated ligamental area, and strong cardinal and lateral teeth ; 
right valve convex. Several sp. Paleozoic; New York. P. 
muricata, Hall. 
PTYCHOPTERIA, Hall, 1893. Differs from Actinoptera in the 
nasute anterior ‘extremity , and large straight wing marked by a 
strong longitudinal fold. 10 sp. Fossil. Chemung Group; 
New York. P. Hugenia, Hall. 
PTERONITELLA. Billings, 1874. 
Distr.—3 sp. U. Silurian; Nova Scotia. P. venuséa, Billings. 
Founded on casts showing in front of the beaks several small, 
anterior cardinal teeth, and close beneath the hinge-line several 
more or less elongated posterior teeth ; there is a strong anterior 
muscular impression, and the whole structure of the hinge 
resembles closely that of Cyrtodonta. 
Hatosta, Bronn, 1830. 
Distr. Hallstadt, Spitzbergen, New Zealand, Cali- 
fornia, Nevada. H. rdrestriata, Mojs. 
Shell semicircular or semioval, with a straight edentulous 
hinge-linge and almost central, scarcely prominent beaks ; valves 
rather compressed, equal, radiately ribbed, the ribs placed close 
to the hinge-line being usually conspicuously thicker than 
others; wings subequal, rounded at their termination and not 
emarginated, muscular scars indistinct. 
The original species described by Bronn is noted as H. salin- 
arum, and is based upon an imperfect specimen, apparently 
restored to a much oblique and inequilateral form. It has the 
anterior wing conspicuously inflated along the hinge-margin, 
and hollow internally. 
DAONELLA, Mojsisovies, 1874. Lateral margins rounded into 
the straight dorsal border; cardinal margin compressed or with 
an oblique furrow on the anterior side, indicating a slight ten- 
dency to form an obscure anterior ‘auricle, defined by the 
faintest possible indication of a marginal sinus. Barely sub- 
generically distinct. D. Lommez, Wissm. (cxxx, 44). 
Monortis, Bronn, 1830. 
Distr.—Trias; Hallein, Himalayas, Thibet, New Zealand, 
United States. J. substriata, Muinst. (cxxx, 45). 
