i: TPTILIAN AGE. JURA SSIC PE RIO D. 



mblanre to C. m-i/nfinn, Meek (Trans. Albany Inst. 1856), a Cretaceous species 

 from Vancouver's Island, l>ut. its truncated posterior margin is more oblique, and 

 its posterior uiiihonal slopes more angular. 



It seems to be more nearly related to the Oolitic species C. aemicostatum, Lycetl 

 (An. Nat. Hist. ls.~>0), hut is longer in proportion to its height, and has less dis-. 

 tiiictly angular nmbonal slopes. The specific name was given in honor of Dr. 

 (Jenrge (i. Shuinard, formerly of the Geological Survey of Texas. 



/..<,///// ,,,,,! jMwi'fltm. Southwest base of the Black Hills, in Jurassic beds, asso- 

 ciated with I:'n in ir,-<>t i* nirtn, Belemites densus, Grammatodon inomatw, &c. (No. 

 191.) 



FAMILY ANATTNIDJE. (See page 3G.) 

 Genus MYACITES (Senior.), MUNSTER. 



Synon. M-jaeita (part.), SCBLOT. Petref. 1820, 176 BHOXS, Leth. 1837, 174. Maitnu, in QOLDF. Petref. Germ. 



II, 1840, 259 WOODWAED, Man. Moll. 1850, 322. Mourn and LTCITT, Moll. Ort. Oolite, 1853, 111. 

 Panopma. (sp.), D'OaiuoxY, Palsont. Fr. Ill, 1844, 329, and of various other* (not Menard de la Groye, 



1809). 

 flruromya, AoAisiz, Etud. Crit. IV, 1845, 231. LEOHH. and BBOKX, Jahrb. 1846, p. 122. CHKVC, llan. 



Conch. II, 1862, 28. 



ifyopiii, AOAIWIZ, Etud. Crit. IV, 1845, 251. Crump, Man. Conch. II, 1862, 28. 

 Kti/m. ftv'f, a mussel. 

 Ezamp. Myarites mviculoitltt, Sen LOT. 



Shell longitiulinally ovate, oblong, or more or less elongate, very thin, nearly or 

 quite equivalve. without a defined lunule ; more or less gibbous in the central and 

 umbonal regions. Extremities gaping, the posterior side more than the anterior, 

 which is often nearly closed. Beaks moderately gibbous, placed between the 

 middle and the anterior extremity. Hinge probably always with one more or less 

 developed cardinal tooth in each valve; cardinal margin sometimes inflected, but 

 more generally erect, excepting near the beaks ; ligament external, short. Valves 

 often with a broad, undefined depression extending from the beaks to the basal or 

 antero-basal margin, usually deepening and widening as it descends. Surface Avith 

 concentric stria?, and often more or less regular concentric ridges or costae, the whole 

 being, when well preserved, usually beset with minute granules. Muscular and 

 pallia! impressions very faintly marked ; sinus of the latter broad and rounded. 



Animal unknown 



There is some confusion in regard to the limits of this genus, some authors 

 including in it a wide range of forms evidently belonging to several genera, while- 

 others restrict it to a few of these, or reject the name entirely, placing the species 

 in one or more of the allied groups. The name Myadtes has perhaps met with less 

 general acceptance because it was not proposed by Schlotheim, who first used it, as 

 the name of a distinct genus, but to designate certain fossil shells supposed by him 

 to belong to the existing genus Mi/a. He merely added the termination ties in this 

 as in other instances, because the species he was figuring and describing were fossils, 

 and not because he supposed them to belong to a new genus. By examining his 

 work, it will be seen he wrote all the names of the genera to which he referred his 



