ni 



, 



III: 



726 



REPORT — 1884. 



In IPS" ihe same author C Zoitschrift dor Deutsclion Gnolngisclien Gesellsclmft,' 

 lid, XXXV., p. 704) has disciis.si'd the relations of Tetraijnttls EifeknsiK, with 

 Dictyophyton, describing mid iihistrutinp iJidyophjifon (rcrolstcinoisis. 



'rhis ^ronp presents a frreat variety oi' form in tlie mode of growtli. Tlv 

 Rtructuro of tlie frond wliich cliaracteriaes every member of tills family, may lie 

 deseribed as a reliculation of liilmlar spicules forming rectangular meshes. In tlif 

 nimpler forms tliese meslies alternate in size and stren^'-th, owinj; to the reguliiv 

 alternation in the size of the bundles of spicules which determine the meshes. In 

 the prismatic and nodose forms, certain bundles of spicules liecome very mucli 

 developed and produce the characteristic form and ornamental ion ot the cup. The 

 middle layer is unifcu'inly reticulate ; while the inner and superficial layer siiow an 

 obli(pie and .s(mietinies a radiate arraiifrement of spicules. In ihe hifjrhly-oiiiaiiicmed 

 .species, the outside layer of spicules is often produced into tufts, spines, aud 

 intersecting (imhria or lamina; of jrreater or less prominence. 



In the foreijrn literature acci'ssible to the writer, there are six species of this 

 family described. In ])re])iirin^- a memoir on tlie subjec't he has been ablo to 

 reco^'jiise, from personal examination, thirty-seven Anierieau forms, tlie ()lilt'>i 

 jreoh)ij:ically beiiifj; iVom the Utica JState, and the latest form from the Keokuk 

 limestone of the Carboniferous system. These thirty-seven sjiecies have lieen 

 described under the followinjr fxenera, viz.: — Cyatlioplivciis, AN'alcott; Dicty- 

 ophyton, ]'-ctenodictya, Lyrodictya, and Pliysospongia, Hall; and Uphantienia, 

 A'amixem. 



2. On ihe Lai)>cUihranchi(ita Fauna of the Upper IFelJerhcrg, ITamM>i\, 

 F()rtniie,Chenuinr/ and Cafsliill Gro7ips (eqnivalenf to the Loicer, iLiJiJh 

 ami Upper ])evo7iiau (if Europe) ; vnlh especial reference to the Arraiujt. 

 ment of ihe Mononiynria and the Derelopment and Dlstrihniion of ihe 

 Species of the Genus Leptodesma. Jhj Profe.ssor Jajii;s Hall, LL.I). 



The investiffaiion of tlie fossil Lamellihranchiate shells has been carried on a?ii 

 part oft he work of thepaheontolop-yof iheState of New York. Already ninety ])late> 

 have been lithofrraphed, and these with their explanations irivin<r the names of tin' 

 fossils have been distributed to the principal sci"entitic societies of iMirope and Aniorica. 

 The full text of the descriptions of tlie species of the Monomyaria, 2(58 pages and 

 plates I.-XXXIII. and liXXXI,- X( ill., have been publislied complete. The re- 

 maininf,' portions of the work are well advanced. 



The Monomyaria are described under twenty-one jrenera and 284 ,'ipecies. Tlie 

 reraainin;,' portion of the work contains illustrations of about 21") species luidev 

 thirty-three genera. 



The author has found it necessary to makesuhdivisions araonjrthe forms U8uanv 

 referred to Aviculopecten, and it has seemed equally impfirtant to pro])Ose other 

 generic names for forms which have heretofore been indiscriminfitely referred to 

 Avicula, I'terinea, Pteronites, vSrc. While the essential internal characters have 

 been rejrarded as of primary ini])ortance, such an arranfrement has been made of the 

 species, that the student may determine tlieir jreneric relations from the general form 

 an<l exterior markings alone. Since, in all forms of the fos.sil Lamellibranchiata the 

 interior surface usually remains attached to the matrix, a reliable means of iden- 

 tifying the geuera by external characters becomes a consideration of pvimavv 

 importance. 



Among the new genera proposed, Leptodesma presents some features in it- 

 develo])ment and distribution wliicli may be of more than ordinary interest. The 

 upper part of the Chemung group exhibits such physical features as might he ex- 

 pected from a gradually shallowing sea and the ap])roach of estuarine condition?. 

 Numerous circumscribed areas appear to iiave existed, and these, while often clmvac- 

 terised by an abundant fauna, contain few species, and these fonns are extremely 

 limited in their geographical range. The species of the genus Leptodesma are often 

 •abundant and very characteristic of certain horizons within limited areas, but rarely 

 have a general distribution through the strata, as some species of the Brachiopoda. 



