724 



SCIENCE. 



[N. S. Vol. II. No. 



tremata it becomes attached to the ventral 

 valve, as in Neotremata. In the two last 

 named orders it modifies the pedicle open- 

 ing. For this and other ontogentic and 

 morphologic characters Owen's terms 

 Lj'Opomata and Arthropomata are aban- 

 doned. The Atremata and Telotremata 

 are provisionally arranged under the super- 

 ordinal term Homocaulia, and Neotremata 

 and Protremata under Idiocaidia. 



A true deltidium is present in the Acrotret- 

 acea of the N'eotremata and in the Protre- 

 mata. 



" The cirrated lophophore, or brachia, is 

 alike in the larval stages of all brachiopods. 

 They first develop tentacles in pairs on each 

 side of the median line in front of the 

 mouth (taxolophus stage). New tentacles 

 are continually added at the same points, 

 until by pushing back the older ones 

 there is a complete circle about the mouth 

 (trocholophus stage), later becoming in- 

 troverted in front (schizolophus stage). 

 From this common and simple structure 

 all the higher types of brachial complica- 

 tion are developed through one of two 

 methods: (1) the growing points of the 

 lophophore, or points at which new ten- 

 tacles are formed, remain in juxtaposition ; 

 or (2) they separate. Complexity in the 

 first is produced (a) by lobation, as in 

 Magathyris, Eiidesella, Baetrynium, Thecidea, 

 etc. (])tycholophus type), and (b) by loop- 

 ing (zuglolophus) and the growth of a me- 

 dian, unpaired coiled arm (plectolophus) , 

 as in Magellania, TerebratuUna, etc.; in the 

 second (c) by the growth of two, separate, 

 coiled extensions or arms, one on each side 

 of the median line (spirolophus), as in 

 lAngula, Crania, Discinisca, Rynchonella , Lep- 

 taina, Davidsonia, Sjnrifer, Athyris, Atrypa, 

 etc." [Charles E. Beecher.] 



Morphological equivalents, or similar 

 structural features, are developed independ- 

 ently, as follows : A spondylium in Obolacea, 

 Lhujulacea, Pentameracea, and rarely in Spirif- 



eracea ; crural processes in Pentameracea and 

 Rynchonellacea ; functional articulation in 

 Protremata and Telotremata ; straight, 

 more or less long, cardinal areas from ros- 

 trate forms in Rynchonellacea, Spiriferacea 

 and Terebratulacea ; rostrate shells ft-om long 

 cardinal areas in Pentameracea ; and loss of 

 pedicle and ventral shell cementation in 

 Craniacea, Stropthomenacea and Spiriferacea. 

 Charles Schuchert. 

 U. S. National Museum. 



ASmO-PHOTOGBAPHIC WORK TO BE CAR- 

 EIED OUT AT COLUMBIA COLLEGE 

 OBSERVATORY. 

 One of the great difficulties that has stood 

 in the way of attaining the highest precision 

 in photographic astrometry has been the de- 

 termination of a possible distortion of the 

 field of the photographic telescope. Some 

 years ago Dr. Gill tried to meet this diflS- 

 culty by recommending the possessors of 

 photographic telescopes to make a series of 

 pictures of the group of stars he had used 

 as comparison stars for the planet Victoria 

 in his Solar Parallax work. These stars 

 had been very carefully determined, both 

 in the meridian and with the heliometer, so 

 that a mere comparison of the photographic 

 coordinates with the others ought to throw 

 considerable light on the question of the 

 optical distortion of the photographic tele- 

 scope. This process has been very carefully 

 carried out by Douner, at the Helsingfors 

 observatory. But the result he has secured 

 leaves the matter still in doubt. His de- 

 termination of the oiitical distortion of the 

 Helsingfors telescope by Gill's method does 

 not possess sufficient weight. The cause of 

 this partial failure of Gill's method must be 

 sought in the unfavorable distribution of 

 the Victoria stars for the purpose in ques- 

 tion, in the small remaining errors of Gill's 

 star positions, the uncertainty of the proper 

 motions, and perhaps also in the low alti- 



